Depsgraph: Fix wrong relations built for drivers

When target was changed from bone to regular object, new dependency graph was
still trying to build relations as if driver was using bone.

source/blender/depsgraph/intern/builder/deg_builder_relations.cc

@@ -1088,7 +1088,10 @@ void DepsgraphRelationBuilder::build_driver_variables(ID *id, FCurve *fcu)
 				continue;
 			}
 			/* Special handling for directly-named bones. */
-			if ((dtar->flag & DTAR_FLAG_STRUCT_REF) && (dtar->pchan_name[0])) {
+			if ((dtar->flag & DTAR_FLAG_STRUCT_REF) &&
+			    (((Object *)dtar->id)->type == OB_ARMATURE) &&
+			    (dtar->pchan_name[0]))
+			{
 				Object *object = (Object *)dtar->id;
 				bPoseChannel *target_pchan =
 				        BKE_pose_channel_find_name(object->pose,