nuv: check ff_rtjpeg_decode_frame_yuv420 return value

CC: libav-stable@libav.org
dv: Add a guard to not overread the ppcm array

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
lavf: fix the comparison in an overflow check

CC: libav-stable@libav.org

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>