Fixes http://samples.mplayerhq.hu/V-codecs/h263/h263-raw/messenger.h263
Fixes regression since b239f3f6

Found-by: Josh Allmann
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit d225b0f7)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>