fix segfault with 'ffmpeg -i 1.avi -cmp 257 -4mv 2.avi'
fix segfault with 'ffmpeg -i 1.avi -cmp 257 -4mv 2.avi'


git-svn-id: a4d7c1866f8397a4106e0b57fc4fbf792bbdaaaf@4178 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

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