nushell: Crash on completion for an alias

Describe the bug

I have an alias to cal. When I try to tab-complete outside of half-complete flags, it crashes.

How to reproduce

1. Have an alias alias calendar = cal --week-start monday.
2. Type calendar and hit tab.

Expected behavior

Normal completion.

Screenshots

No response

Configuration

key	value
version	0.91.0
branch	main
commit_hash	3016d7a64ccb2c2eac9f735f6144fc896ea724a5
build_os	linux-x86_64
build_target	x86_64-alpine-linux-musl
rust_version	rustc 1.76.0 (07dca489a 2024-02-04) (Alpine Linux 1.76.0-r1)
cargo_version	cargo 1.76.0
build_time	2024-03-06 15:32:43 +03:00
build_rust_channel	debug
allocator	mimalloc
features	default, sqlite, trash, which, zip
installed_plugins

Additional context

Backtrace

~/fork/nushell> calendar Error:   × Main thread panicked.
  ├─▶ at crates/nu-cli/src/completions/command_completions.rs:99:43
  ╰─▶ attempt to subtract with overflow
         0: 0x56021407ba00 - rust_begin_unwind
         1: 0x560211417275 - core::panicking::panic_fmt::h914dbe9d19fb3535
         2: 0x560211417333 - core::panicking::panic::ha1e97a8c9b8dbf22
         3: 0x5602128b9156 -
      nu_cli::completions::command_completions::CommandCompletion::complete_commands
      ::{{closure}}::h90df70ef45a6d236
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/command_completions.rs:99
         4: 0x5602128adf3e - core::iter::adapters::map::map_fold::
      {{closure}}::h5a4864bec900b524
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/iter/adapters/map.rs:85
         5: 0x5602128a4e92 -
      core::iter::traits::iterator::Iterator::fold::h1d8fcd0ac6e85bb6
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/iter/traits/iterator.rs:2640
         6: 0x5602128a8bdf - <core::iter::adapters::map::Map<I,F> as
      core::iter::traits::iterator::Iterator>::fold::h253d84410d4f3d4d
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/iter/adapters/map.rs:125
         7: 0x5602128ac9d8 -
      core::iter::traits::iterator::Iterator::for_each::h24bdee46414a669f
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/iter/traits/iterator.rs:858
         8: 0x5602128fbcf5 - alloc::vec::Vec<T,A>::extend_trusted::he7e74c7be83d089a
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      alloc/src/vec/mod.rs:2923
         9: 0x56021290461b - <alloc::vec::Vec<T,A> as
      alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend::hafe212401d087fbf
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      alloc/src/vec/spec_extend.rs:26
        10: 0x5602128f921a - <alloc::vec::Vec<T> as
      alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::hce085
      215ac09c056
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      alloc/src/vec/spec_from_iter_nested.rs:62
        11: 0x560212900a6e - alloc::vec::in_place_collect::<impl
      alloc::vec::spec_from_iter::SpecFromIter<T,I> for
      alloc::vec::Vec<T>>::from_iter::h4b8c5e6f0cb0445b
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      alloc/src/vec/in_place_collect.rs:237
        12: 0x560212903fa7 - <alloc::vec::Vec<T> as
      core::iter::traits::collect::FromIterator<T>>::from_iter::h42637383c7969e1e
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      alloc/src/vec/mod.rs:2791
        13: 0x5602128ac70e -
      core::iter::traits::iterator::Iterator::collect::h63471a478d06ba86
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/iter/traits/iterator.rs:2054
        14: 0x5602128e0a19 -
      nu_cli::completions::command_completions::CommandCompletion::complete_commands
      ::h42df181777a3d104
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/command_completions.rs:91
        15: 0x5602128e1449 -
      <nu_cli::completions::command_completions::CommandCompletion as
      nu_cli::completions::base::Completer>::fetch::he5f5646cdcd08316
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/command_completions.rs:174
        16: 0x5602128bf554 -
      nu_cli::completions::completer::NuCompleter::process_completion::h1d7275f0be0e
      89aa
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/completer.rs:51
        17: 0x5602128d8839 -
      nu_cli::completions::completer::NuCompleter::completion_helper::hd263b8895ae68
      5a4
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/completer.rs:359
        18: 0x5602128d92c4 - <nu_cli::completions::completer::NuCompleter as
      reedline::completion::base::Completer>::complete::hc0d89a76e5caef80
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/
      completions/completer.rs:416
        19: 0x5602128bf195 -
      reedline::completion::base::Completer::complete_with_base_ranges::h88d6d236ed4
      9ce28
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/completion/base.rs:45
        20: 0x560212aeddcf - <reedline::menu::columnar_menu::ColumnarMenu as
      reedline::menu::Menu>::update_values::ha0ae642bc0fca99f
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/menu/columnar_menu.rs:497
        21: 0x560212adc75d -
      reedline::menu::ReedlineMenu::update_values::h716045a7d0d19857
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/menu/mod.rs:334
        22: 0x560212a31abe -
      reedline::engine::Reedline::handle_editor_event::h43f080a14074c43c
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/engine.rs:924
        23: 0x560212a3167e -
      reedline::engine::Reedline::handle_editor_event::h43f080a14074c43c
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/engine.rs:1232
        24: 0x560212a2de6d -
      reedline::engine::Reedline::handle_event::hdf54c8b3e0974f93
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/engine.rs:799
        25: 0x560212a2d567 -
      reedline::engine::Reedline::read_line_helper::h6eb92ca7a94c7c16
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/engine.rs:774
        26: 0x560212a2ca40 - reedline::engine::Reedline::read_line::h0eae5bcfcfd36ecc
                      at /home/kaathewise/.local/state/cargo/registry/src/
      index.crates.io-6f17d22bba15001f/reedline-0.30.0/src/engine.rs:633
        27: 0x5602128c73a9 - nu_cli::repl::loop_iteration::h2594b2cf01789510
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:463
        28: 0x5602128d4725 - nu_cli::repl::evaluate_repl::
      {{closure}}::hf0983c49275ae83b
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:139
        29: 0x56021290f6ff - <core::panic::unwind_safe::AssertUnwindSafe<F> as
      core::ops::function::FnOnce<()>>::call_once::h6107931275d50bc4
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/panic/unwind_safe.rs:272
        30: 0x560212906ab0 - std::panicking::try::do_call::hb158827e2d6f5e15
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      std/src/panicking.rs:552
        31: 0x560212906b8b - __rust_try
        32: 0x5602129069ad - std::panicking::try::haa1bc36603962107
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      std/src/panicking.rs:516
        33: 0x5602128de1ee - std::panic::catch_unwind::h56042bac87a17784
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      std/src/panic.rs:142
        34: 0x5602128c418b - nu_cli::repl::evaluate_repl::hf0503d4f1b546231
                      at /home/kaathewise/fork/nushell/crates/nu-cli/src/repl.rs:138
        35: 0x560211433c0c - nu::run::run_repl::h2c2973aec0f47a2c
                      at /home/kaathewise/fork/nushell/src/run.rs:273
        36: 0x56021145a830 - nu::main::hcbba518c96dbe3ac
                      at /home/kaathewise/fork/nushell/src/main.rs:353
        37: 0x56021145db4b -
      core::ops::function::FnOnce::call_once::h305e3e4bbe292faf
                      at /rustc/07dca489ac2d933c78d3c5158e3f43beefeb02ce/library/
      core/src/ops/function.rs:250
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.