This is:
 - what Posix says (-1 on error, >=0 on success)
 - fixing a bug on winCE (<0 sometimes)

Patch by Martin Storsjö: martin martin st


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@19513 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b