Fixes out of array accesses
Fixes: ffmpeg_mjpeg_crash.avi
Found-by: Thomas Lindroth <thomas.lindroth@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 08509c8f)

Conflicts:

	libavcodec/mjpegdec.c
(cherry picked from commit 0861bb66d7c281c92a0746167bb141735a660856)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>