The original code for viewlayer collection flag syncing across moves
from D9158 didn't consider the case where the collection could no longer
be found in its original view layer (moving a collections betwen scenes).

The fix is to just check if the collection starts in the same scene as
it will be moved to before trying to do the flag syncing.

I thought about this for a while and tried a couple other solutions, but
I couldn't come up with a proper way to support syncing the layer
collection flags across scenes without making too many changes.
P1769 seems to work, but I couldn't figure out exactly why, which
scares me a bit, so instead this patch just disables the flag syncing
in this case.