lavf/segment: add segment_list_entry_prefix option

This option allows to add a prefix to the segment list entry filenames.

Also set by default the list entry filenames to the corresponding
segment basename, consistent with the HLS muxer.

Based on an idea by Steven Liu <lingjiujianke@gmail.com>.
lavf/segment: add a few log messages when avio_open2() fails
ffprobe: add support for subtitle frames

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
Revert "Merge remote-tracking branch 'qatar/master'" (43dec5ef9a360c9ffac3278f464832bd99af0cb0)

Fixes out of array accesses
Fixes asan_static-oob_eb9812_5961_iv41.avi
This reverts the merge of c9ef6b09326a24010bf86d6b0d19cfa42df4d546

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind