Blender Git Loki

Fix T59220: Deleting object causes blender 2.8 to crash

The issue was caused by a special code in node tree freeing function
which will free extra fields in the case when tree is not in bmain.
This is how old code was dealing with "nested" trees, but is now
making behavior different from other datablocks. This is exactly
what was confusing copy-on-write logic.

Ideally, ntreeFreeTree() need to behave same as all other datablocks,
ad freeing of data of nested trees should be up to the owner of the
tree (this way it's all explicit and does not depend on check of
some special flag.