44510662e9
Code was using seq->start + seq->len to figure out where the "right
side of content" is, seemingly since forever (i.e. since 997b5fe4
added strip thumbnails). But that is incorrect starting with 3.3,
where seq->len is "number of frames / samples in source media",
but that does not necessarily match number of frames in the timeline.
For movies this happens when media framerate does not match
sequencer framerate.
Use SEQ_time_content_end_frame_get instead to calculate where the
content ends.
Pull Request: https://projects.blender.org/blender/blender/pulls/124081