`seq_free_animdata()` removes fcurve pointers belonging to strips from
`Scene` CoW datablock's `AnimData` during `BKE_scene_graph_update_for_newframe`.
This causes problems with updating animation.
This worked before rBbe2e41c397ba, because `AnimData` was freed by `BKE_animdata_free()`
before `seq_free_animdata()` was executed, so it had no data to operate on and returned
on precondition `if (scene->adt == NULL || scene->adt->action == NULL)`
Reviewed By: mont29, brecht
Maniphest Tasks: T74897
Differential Revision: https://developer.blender.org/D7264
77ca5ab6b0