avfilter/avcodec: use NULL instead of 0 for pointer

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc_ps: Add context to av_log() call

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/buffersrc: add context to av_log() call

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