Only a return value of -1 indicates an error for open(),
purely theoretically the mixer device could get 0 assigned
as file descriptor.
Even more theoretically, WinCE uses descriptors with values < 0,
though that probably is non-conformant behaviour.
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@35295 b3059339-0415-0410-9bf9-f77b7e298cf2