Fix T49229: ID user decrement error when deleting group instance twice.

Another great example of inconsistency in usercount handling - dupli_group was considered
as refcounted by readfile.c code (and hence by library_query.c one, which is based on it),
but not by editor/BKE_object code, which never increased group's usercount when creating
an instance of it etc.

To be backported to 2.78.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/editors/object/object_edit.c b/source/blender/editors/object/object_edit.c
index 3dc7d8ebd4b..111afcdc7a7 100644
--- a/source/blender/editors/object/object_edit.c
+++ b/source/blender/editors/object/object_edit.c
@@ -910,7 +910,7 @@ static void copy_attr(Main *bmain, Scene *scene, View3D *v3d, short event)
 
 					base->object->dup_group = ob->dup_group;
 					if (ob->dup_group)
-						id_lib_extern(&ob->dup_group->id);
+						id_us_plus(&ob->dup_group->id);
 				}
 				else if (event == 7) {    /* mass */
 					base->object->mass = ob->mass;