Limit the scope of a local variable in a helper function.

Cython/Utility/ExtensionTypes.c

@@ -340,7 +340,6 @@ static CYTHON_INLINE PyObject *{{func_name}}_maybe_call_slot(PyTypeObject* type,
 }
 
 static PyObject *{{func_name}}(PyObject *left, PyObject *right {{extra_arg_decl}}) {
-    PyObject *res;
     int maybe_self_is_left, maybe_self_is_right = 0;
     maybe_self_is_left = Py_TYPE(left) == Py_TYPE(right)
 #if CYTHON_USE_TYPE_SLOTS
@@ -356,6 +355,7 @@ static PyObject *{{func_name}}(PyObject *left, PyObject *right {{extra_arg_decl}
                 || __Pyx_TypeCheck(right, {{type_cname}});
     }
     if (maybe_self_is_left) {
+        PyObject *res;
         if (maybe_self_is_right && !{{overloads_left}}) {
             res = {{call_right}};
             if (res != Py_NotImplemented) return res;