Blender Git Loki

Fix wrong tracking curves after changing clip offset

The issue was caused by frame start/offset change triggering clip
reload, which was happening with a hardcoded scene frame index of 1,
which could be outside of the actual clip frames.

Solved by removing source change tag from the frame start/offset
update. The source doesn't really change: the resolution will stay
the same, as well as media type, its duration. So the tag was not
needed.