Blender Git Loki

Fix (unreported) potential assert in viewlayer synchronization.

Some operations, like remapping and ID (Object) to another, can lead to
having the same object in more than one base.

While this is not a valid state, this is being taken care of by the
`BKE_layer_collection_sync` call, so the object-to-base GHash generation
itself should be resilient to such issue.

Note: another way to fix this would be to make remapping post-process
code check explicitely for such doublons, but I would rather avoid
adding even more 'specialized' code there, it already has to deal with
too many of those corner cases.