Add missing error checks for usages of PyIter_Next

[WolframAlph]

Bug report

Bug description:

Not all usages of PyIter_Next in the codebase comply with specified behavior:

cpython/Objects/abstract.c

Lines 2905 to 2919 in 180d417

	/* Return next item.
	*
	* If an error occurs, return NULL. PyErr_Occurred() will be true.
	* If the iteration terminates normally, return NULL and clear the
	* PyExc_StopIteration exception (if it was set). PyErr_Occurred()
	* will be false.
	* Else return the next object. PyErr_Occurred() will be false.
	*/
	PyObject *
	PyIter_Next(PyObject *iter)
	{
	PyObject *item;
	(void)iternext(iter, &item);
	return item;
	}

.
One example would be:

cpython/Objects/frameobject.c

Lines 246 to 268 in 180d417

	while ((key = PyIter_Next(iter)) != NULL) {
	value = PyObject_GetItem(other, key);
	if (value == NULL) {
	Py_DECREF(key);
	Py_DECREF(iter);
	return -1;
	}
	if (framelocalsproxy_setitem(self, key, value) < 0) {
	Py_DECREF(key);
	Py_DECREF(value);
	Py_DECREF(iter);
	return -1;
	}
	Py_DECREF(key);
	Py_DECREF(value);
	}
	Py_DECREF(iter);
	return 0;
	}

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-128198: Add missing error checks for usages of PyIter_Next #128199