avformat/ico: use avmalloc(z)_array()

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

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

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