DVD PTS discontinuities are now handled by 'flattening' the timecodes of incoming packets. This prevents AVFormatDecoder getting stuck buffering video frames when the timecodes jump backwards.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
(cherry picked from commit b6c0ec5529d8b921a846c38b5d6afeb06a4d5671)

Refs #11371