avdevice/iec61883: Use av_freep(), avoid leaving stale pointers in memory

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

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

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