cmd: ensure create_full_path returns FALSE for all errors

[Dan Kegel]

2011/6/4 Dan Kegel <dank at kegel.com>:
> https://testbot.winehq.org/JobDetails.pl?Key=11484
> It passes on all tested platforms.  Feel free to
> submit along with your patch verbatim if it looks
> sufficient to you.

BTW it looks like cmd test suite completely ignores
stderr, which explains why that test passes even though
the error message produced by wine's cmd and native cmd
are different.