avcodec/cngenc: Use av_malloc_array()

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

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/pthread: Use av_mallocz_array()

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

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