Fix for random crash in localized node group freeing while tweaking

group default values.

This can happen when using value sliders for node group input values.
The localized copies were setting the "interface_type" runtime pointer
of the original tree to NULL instead of the new tree (which is created
on-the-fly in general). This type is used in RNA update functions
however, the original tree DNA should not be modified there.

source/blender/blenkernel/intern/node.c

@@ -1204,7 +1204,7 @@ static bNodeTree *ntreeCopyTree_internal(bNodeTree *ntree, Main *bmain, bool do_
 	}
 	
 	/* node tree will generate its own interface type */
-	ntree->interface_type = NULL;
+	newtree->interface_type = NULL;
 	
 	return newtree;
 }