pwndbg: Heap heuristics may crash if libc.so is dynamically linked but no symbols are present for it

This is weird:

dc@jhtc:~$ gdb --quiet -ex 'set context-sections ""' -ex 'set auto-solib-add off' -ex 'set resolve-heap-via-heuristic on' -ex 'entry' /bin/ls
pwndbg: loaded 207 commands. Type pwndbg [filter] for a list.
pwndbg: created $rebase, $ida gdb functions (can be used with print/break)
Reading symbols from /bin/ls...
(No debugging symbols found in /bin/ls)
Sections set to be empty. FYI valid values are: regs, disasm, args, code, stack, backtrace, expressions, ghidra
You are going to resolve the heap via heuristic. This might not work in all cases.
You are going to resolve the heap via heuristic. This might not work in all cases.
Temporary breakpoint 1 at 0x555555559850
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Temporary breakpoint 1, 0x0000555555559850 in ?? ()
------- tip of the day (disable with set show-tips off) -------
Pwndbg context displays where the program branches to thanks to emulating few instructions into the future. You can disable this with set emulate off which may also speed up debugging
You are going to resolve the heap via heuristic. This might not work in all cases.
pwndbg> set exception-verbose on
Set whether to print a full stacktrace for exceptions raised in Pwndbg commands to True
pwndbg> heap
Traceback (most recent call last):
  File "/opt/pwndbg/pwndbg/commands/__init__.py", line 147, in __call__
    return self.function(*args, **kwargs)
  File "/opt/pwndbg/pwndbg/commands/__init__.py", line 218, in _OnlyWhenRunning
    return function(*a, **kw)
  File "/opt/pwndbg/pwndbg/commands/__init__.py", line 273, in _OnlyWithResolvedHeapSyms
    return function(*a, **kw)
  File "/opt/pwndbg/pwndbg/commands/__init__.py", line 243, in _OnlyWhenHeapIsInitialized
    return function(*a, **kw)
  File "/opt/pwndbg/pwndbg/commands/heap.py", line 126, in heap
    heap_region = allocator.get_heap_boundaries(addr)
  File "/opt/pwndbg/pwndbg/heap/ptmalloc.py", line 1717, in get_heap_boundaries
    arena = self.get_arena(addr)
  File "/opt/pwndbg/pwndbg/heap/ptmalloc.py", line 1703, in get_arena
    return self.main_arena
  File "/opt/pwndbg/pwndbg/heap/ptmalloc.py", line 885, in main_arena
    elif self.is_glibc_static_symbol(main_arena_via_symbol):
  File "/opt/pwndbg/pwndbg/heap/ptmalloc.py", line 872, in is_glibc_static_symbol
    _IO_list_all_addr = pwndbg.symbol.address("_IO_list_all")
  File "/opt/pwndbg/pwndbg/lib/memoize.py", line 51, in __call__
    value = self.func(*args, **kwargs)
  File "/opt/pwndbg/pwndbg/symbol.py", line 215, in address
    address = int(re.search("0x[0-9a-fA-F]+", result).group(), 0)
AttributeError: 'NoneType' object has no attribute 'group'

If that is an issue, you can report it on https://github.com/pwndbg/pwndbg/issues
(Please don't forget to search if it hasn't been reported before)
To generate the report and open a browser, you may run `bugreport --run-browser`
PS: Pull requests are welcome
pwndbg>