mmvideo/mm_decode_inter: check horizontal coordinate too

Fixes out of array accesses

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mmvideo/mm_decode_intra: check horizontal coordinate too

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>