avcodec/pgssubdec: Use av_malloc(z)_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/proresdec2: Use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avdevice/v4l2: Use av_malloc_array()

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