cmd: ensure create_full_path returns FALSE for all errors

[Frédéric Delanoy]

2011/6/4 Dan Kegel <dank at kegel.com>:
> (Oddly, windows xp's cmd doesn't seem to set errorlevel
> if you use rmdir on a nonexistent directory...)

Yep. Exactly the same in w2k... yet another Windows oddity...