h264: Add signed casts to avoid MSVC C4146 error.
h264: Add signed casts to avoid MSVC C4146 error.

canbal/l-smash,l-smash/l-smash,dwbuiten/l-smash,canbal/l-smash,l-smash/l-smash,maki-rxrz/L-SMASH,silverfilain/L-SMASH,l-smash/l-smash,silverfilain/L-SMASH,maki-rxrz/L-SMASH,dwbuiten/l-smash,silverfilain/L-SMASH