avcodec/fft-test: use av_malloc_array()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/psymodel: use av_malloc(z)_array()

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

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