src: unclutter command_default function

src: unclutter command_default function

(Essentially, 5 levels of indentation have been stripped compared to the
original layout, and this is surely a result that looks a lot better
than it did before.)

Things to note:

1. If the m->parse call succeeded, we can return from the function and
do not need to go through the other code. As such, "m" is guaranteed to
be useless at the end of the match loop, and so, conditions can be
removed.

2. Since the per-extension parse function only ever get their own option
codes (since v1.4.10-26-gd09b6d5), their return value no longer has a
meaning and can be ignored.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>