Blender Git Loki

Fix T77847: "Add plane > align" causes crash when certain rigs are in the scene (2.83, fixed in 2.90).

Root of the issue was not fixed in 2.90, only hidden by the fact that we
now re-read much less data during undo's that we used to, when some new
datablock gets added or removed.

This is not an ideal solution (as usual when dealing with data pointers
shared across data-blocks), but it's decent enough. thanks a lot to
@brecht for it!

To be backported to 2.83 too.