Blender Git Loki

Fix T50013: Blender 2.78a Link/Append Crash.

Object freeing may in some kind access its obdata (in case it has some
caches e.g.), since here obdata may have already been freed, let's set
object's data pointer to NULL (probably not ideal solution, but we don't
care much, those form archipelagos of unused linked datablocks,
we nuke'em all anyway).

Also fix stupid mistake in one of own recent commits (using ID we just
freed, tsst...).