vp3: Check the framerate for validity

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 6fc8226e29055858f28973bb3d27b63b3b65e616)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit b4c479a82adbb1301e3e549cd80cdd65208ddd05)
svq3: Check for any negative return value from ff_h264_check_intra_pred_mode

Also pass on any returned error code.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 1115689d54ea95a084421f5a182b8dc56cbff978)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

Conflicts:
	libavcodec/svq3.c