fix relationship line always drawing from the parents origin

this can be different though (e.g. vertex parenting) and correct location
is already stored in ob->orig

spotted while looking into T59332

Reviewers: fclem, brecht

Differential Revision: https://developer.blender.org/D4076

source/blender/draw/modes/object_mode.c

@@ -2271,7 +2271,7 @@ static void DRW_shgroup_relationship_lines(
         Object *ob)
 {
 	if (ob->parent && DRW_object_is_visible_in_active_context(ob->parent)) {
-		DRW_shgroup_call_dynamic_add(sgl->relationship_lines, ob->parent->obmat[3]);
+		DRW_shgroup_call_dynamic_add(sgl->relationship_lines, ob->orig);
 		DRW_shgroup_call_dynamic_add(sgl->relationship_lines, ob->obmat[3]);
 	}