Previously code that was reading Strip data assumed that seqbasep
and channels members would stay at fixed offsets within a struct,
forever into the future. Fix this by inferring their offsets from
the file SDNA data where needed.
Actual Strip DNA layout is not changed in this commit yet.
Co-authored-by: Sergey Sharybin <sergey@blender.org>
Pull Request: https://projects.blender.org/blender/blender/pulls/142940
