ffprobe: free shared writer context on exit

Fix leak.

Spotted-by: Michael Niedermayer
avformat/utils: Fix pts_wrap_behavior calculation with negative first_dts

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/utils: also fix wrapping of start_time in update_initial_timestamps()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/utils: correct for timestamp wrap earlier

This uses dts & pts as reference instead of first_dts

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mpegts: do not set pts for missing dts in video streams

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