Fix memory leak in armatures with no bones

The cleanup operation was never run for such armatures.

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

@@ -337,7 +337,9 @@ void DepsgraphRelationBuilder::build_rig(Object *object)
 	                          NodeType::PARAMETERS,
 	                          OperationCode::ARMATURE_EVAL);
 	add_relation(armature_key, pose_init_key, "Data dependency");
-	/* IK Solvers.
+	/* Run cleanup even when there are no bones. */
+	add_relation(pose_init_key, pose_cleanup_key, "Init -> Cleanup");
+		/* IK Solvers.
 	 *
 	 * - These require separate processing steps are pose-level to be executed
 	 *   between chains of bones (i.e. once the base transforms of a bunch of