Fix ref-antileak in _struct.c which eventually lead to deallocating None.
diff --git a/Modules/_struct.c b/Modules/_struct.c
index cb2e538..add5e8c 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1513,7 +1513,7 @@
 		return NULL;
 	}
 
-	return Py_None;
+	Py_RETURN_NONE;
 }
 
 static PyObject *