Set C predictor to zero if unavailable (should fix B-frame border artifacts)
Set C predictor to zero if unavailable (should fix B-frame border artifacts)

git-svn-id: a4d7c1866f8397a4106e0b57fc4fbf792bbdaaaf@8702 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

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