core: handle FileNotFound error when launching commands

Gracefuly handle errors when attempting to launch a command that does
not exist by catching the exception and returning the expected status
code and program output. The exception text is returned as "stderr".

This prevents errors when aspell is enabled on systems that do not have
the `aspell` binary installed.

Signed-off-by: David Aguilar <davvid@gmail.com>

Author: davvid

cola/core.py

@@ -273,7 +273,10 @@ def run_command(cmd, *args, **kwargs):
 
     """
     encoding = kwargs.pop('encoding', None)
-    process = start_command(cmd, *args, **kwargs)
+    try:
+        process = start_command(cmd, *args, **kwargs)
+    except FileNotFoundError as err:
+        return (EXIT_UNAVAILABLE, UStr('', ENCODING), UStr(f'{err}', ENCODING))
     (output, errors) = communicate(process)
     output = decode(output, encoding=encoding)
     errors = decode(errors, encoding=encoding)