avformat/id3v2: Use av_freep() avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/http: Use av_freep() avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/mmst: Use av_freep() avoid leaving stale pointers in memory

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