Crash could could happen if `Clip Display` > `Render Undistorted` was
enabled on a clip, but the clip then unlinked (code was accessing the
clips `MovieTracking` for garbage memory then).
To resolve, just check the clip prior.
NOTE: there are similar other checks (e.g. in `spline_under_mouse_get`)
that actually check the clip prior.
Pull Request: https://projects.blender.org/blender/blender/pulls/121203
7d70942a84