Blender Git Loki

Fix T68647: objects cannot be moved to collection if there is no active
object

This showed e.g. when deleting active object, then selecting using box
select.
This commit also lifts the restriction that linked objects could not be
moved to a collection.

Reviewers: campbellbarton, dfelinto

Maniphest Tasks: T68647

Differential Revision: https://developer.blender.org/D5485