Kernel hangs if invalid shell command is entered

[sohang3112]

For example, if an invalid shell command !lsd is entered in a cell, kernel hangs due to uncaught error:

Traceback (most recent call last):
  File "/home/sohang/.local/lib/python3.10/site-packages/ipykernel/kernelbase.py", line 412, in dispatch_shell
    await result
  File "/home/sohang/.local/lib/python3.10/site-packages/ipykernel/kernelbase.py", line 731, in execute_request
    reply_content = self.do_execute(
  File "/mnt/d/iforth/forth_kernel/forth_kernel.py", line 113, in do_execute
    self.answer_text(check_output(code[1:], encoding='utf-8'), 'stdout')
  File "/usr/lib/python3.10/subprocess.py", line 421, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/lib/python3.10/subprocess.py", line 503, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/lib/python3.10/subprocess.py", line 971, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.10/subprocess.py", line 1863, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'lsd'