Fix #34115, Group Node corrupted by frames.

The group node operators offset nodes when moving them between node trees, but this should only be done for "free", un-parented nodes not attached to a frame, otherwise the node loc is relative to the parent node.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54354 954f8c5b-7b00-dc11-b283-0030488c597c