open(2) returns -1 on error (if the device does not exist),
and -1 is true.

Also, put shank's name in the copyright header since half
the code is his (including this bug :P).

git-svn-id: https://svn.musicpd.org/mpd/trunk@4310 09075e82-0dd4-0310-85a5-a0d7c8717e4f