avcodec/vp9: Use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
huffyuvenc: write last odd sample

If width is odd, last sample wouldn't be written.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
huffyuvdec: decode the last odd sample

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