Simplify example of PyErr_Fetch() use

Doc/extending/newtypes.rst

@@ -962,9 +962,8 @@ done.  This can be done using the :c:func:`PyErr_Fetch` and
 
        if (self->my_callback != NULL) {
            PyObject *err_type, *err_value, *err_traceback;
-           int have_error = PyErr_Occurred() ? 1 : 0;
 
-           if (have_error)
+           /* This saves the current exception state */
            PyErr_Fetch(&err_type, &err_value, &err_traceback);
 
            cbresult = PyObject_CallObject(self->my_callback, NULL);
@@ -973,7 +972,7 @@ done.  This can be done using the :c:func:`PyErr_Fetch` and
            else
                Py_DECREF(cbresult);
 
-           if (have_error)
+           /* This restores the saved exception state */
            PyErr_Restore(err_type, err_value, err_traceback);
 
            Py_DECREF(self->my_callback);