alacritty: 3-byte crash

alacritty crashes when I issue the following command:

echo 6KWe | base64 -d

Found by catting the /dev/urandom again. (Might be related to #499 .)

Backtrace:

thread 'main' panicked at 'index 25 out of range for slice of length 24', /checkout/src/libcore/slice/mod.rs:672

stack backtrace:
stack backtrace:
   0:     0x55f7c9786e23 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hab274209b3900f9c
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x55f7c9783034 - std::sys_common::backtrace::_print::h8f655fc4b25b9b70
                               at /checkout/src/libstd/sys_common/backtrace.rs:71
   2:     0x55f7c978cc37 - std::panicking::default_hook::{{closure}}::hd0f0fde26cdd4a91
                               at /checkout/src/libstd/sys_common/backtrace.rs:60
                               at /checkout/src/libstd/panicking.rs:355
   3:     0x55f7c978c7fc - std::panicking::default_hook::h123df66825ae8c79
                               at /checkout/src/libstd/panicking.rs:371
   4:     0x55f7c978d10b - std::panicking::rust_panic_with_hook::h3635757261b59272
                               at /checkout/src/libstd/panicking.rs:549
   5:     0x55f7c978cfe4 - std::panicking::begin_panic::he3b450c9ca51fd2b
                               at /checkout/src/libstd/panicking.rs:511
   6:     0x55f7c978cf19 - std::panicking::begin_panic_fmt::hf44dbae7fe247adf
                               at /checkout/src/libstd/panicking.rs:495
   7:     0x55f7c978cea7 - rust_begin_unwind
                               at /checkout/src/libstd/panicking.rs:471
   8:     0x55f7c97b7ded - core::panicking::panic_fmt::hde6a1a29c4abc8e6
                               at /checkout/src/libcore/panicking.rs:69
   9:     0x55f7c97b7ee9 - core::slice::slice_index_len_fail::h8d6a353e66085a31
                               at /checkout/src/libcore/slice/mod.rs:672
  10:     0x55f7c9737e47 - <core::ops::Range<usize> as core::slice::SliceIndex<[T]>>::index::ha12f7058d2f2ddad
                               at /checkout/src/libcore/slice/mod.rs:803
  11:     0x55f7c972aace - core::slice::<impl core::ops::Index<I> for [T]>::index::h19b918c17299cb0b
                               at /checkout/src/libcore/slice/mod.rs:654
  12:     0x55f7c973b4d2 - font::ft::FreeTypeRasterizer::get_rendered_glyph::ha10889efce849e32
                               at /home/amozes/workspace/github/alacritty/font/src/ft/mod.rs:217
  13:     0x55f7c973b029 - font::ft::FreeTypeRasterizer::get_rendered_glyph::ha10889efce849e32
                               at /home/amozes/workspace/github/alacritty/font/src/ft/mod.rs:194
  14:     0x55f7c973992d - <font::ft::FreeTypeRasterizer as font::Rasterize>::get_glyph::h865be892ed938886
                               at /home/amozes/workspace/github/alacritty/font/src/ft/mod.rs:85
  15:     0x55f7c92e8ed6 - alacritty::renderer::GlyphCache::get::{{closure}}::h25eb2135d53f0bf2
                               at /home/amozes/workspace/github/alacritty/src/renderer/mod.rs:270
  16:     0x55f7c92a286a - <std::collections::hash::map::Entry<'a, K, V>>::or_insert_with::h64977a0049ce1560
                               at /checkout/src/libstd/collections/hash/map.rs:1936
  17:     0x55f7c92e8dd6 - alacritty::renderer::GlyphCache::get::h533abf2b25792cdc
                               at /home/amozes/workspace/github/alacritty/src/renderer/mod.rs:267
  18:     0x55f7c92ec19c - alacritty::renderer::RenderApi::render_cells::h709352b1c43cc71b
                               at /home/amozes/workspace/github/alacritty/src/renderer/mod.rs:785
  19:     0x55f7c92e4b1e - alacritty::display::Display::draw::{{closure}}::hf31aab8dbf3ee1a0
                               at /home/amozes/workspace/github/alacritty/src/display.rs:299
  20:     0x55f7c92ea775 - alacritty::renderer::QuadRenderer::with_api::h6adcf7ff439417bb
                               at /home/amozes/workspace/github/alacritty/src/renderer/mod.rs:610
  21:     0x55f7c92e4734 - alacritty::display::Display::draw::h86ecf4d9d58d2ac0
                               at /home/amozes/workspace/github/alacritty/src/display.rs:297
  22:     0x55f7c915bcdd - alacritty::run::h1531f576730b74a1
                               at /home/amozes/workspace/github/alacritty/src/main.rs:172
  23:     0x55f7c915a57c - alacritty::main::hb27efce3c2542868
                               at /home/amozes/workspace/github/alacritty/src/main.rs:64
  24:     0x55f7c979405a - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:98
  25:     0x55f7c978d8aa - std::rt::lang_start::ha5350a26f8f175ab
                               at /checkout/src/libstd/panicking.rs:433
                               at /checkout/src/libstd/panic.rs:361
                               at /checkout/src/libstd/rt.rs:57
  26:     0x55f7c915c322 - main
  27:     0x7fbd4fc78290 - __libc_start_main
  28:     0x55f7c90b47a9 - _start
  29:                0x0 - <unknown>