Take the gap logic from mpegtsdemux, and don't send gap events on a stream that's outputting buffers with no timestamps. Time isn't advancing, but the stream has buffers - so it's not sparse. Fixes #2374 Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4333>
It's possibly timestamp rollover case. But PTS < DTS is already invalid case anyway. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3657>