Simplify error checking using Zackery Spytz suggestion

Author: Rémi Lapeyre

Parser/asdl_c.py

@@ -702,7 +702,7 @@ def visitModule(self, mod):
         while (PyDict_Next(kw, &i, &key, &value)) {
             PyObject* pos = _PyObject_FastCallDict(index, &key, 1, NULL);
             PyObject* err = PyErr_Occurred();
-            if (pos == NULL || err != NULL) {
+            if (pos == NULL) {
                 // arbitrary keyword arguments are accepted
                 if (!PyErr_GivenExceptionMatches(err, PyExc_ValueError)) {
                     res = -1;