Caused by {rB571362642201} where versioning code for new sequencer tool
settings was only done for scenes already having sequencer scene->ed.
If scene->ed was not present, sequencer tool settings were never
initalized for this scene [if the VSE was then used later], leading to
crashes in some places.
Now just use the versioning code to initalize sequencer tool settings
for all scenes not having them yet.
Maniphest Tasks: T87010
Differential Revision: https://developer.blender.org/D10996
0f81dafe6c