Mention in the documentation of avfilter_poll_frame() that it returns a negative value in case of error.
Mention in the documentation of avfilter_poll_frame() that it returns
a negative value in case of error.


git-svn-id: a4d7c1866f8397a4106e0b57fc4fbf792bbdaaaf@16372 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

prajnashi/ffmpeg,prajnashi/ffmpeg,prajnashi/ffmpeg,prajnashi/ffmpeg