Do not DECREF tuple until tuple items are no longer used

[radarhere]

Pillow/src/encode.c

Lines 767 to 777 in 2c3a977

	item = PyList_GetItemRef(tags, pos);
	if (item == NULL) {
	Py_DECREF(encoder);
	return NULL;
	}
	// We already checked that tags is a 2-tuple list.
	key = PyTuple_GET_ITEM(item, 0);
	key_int = (int)PyLong_AsLong(key);
	value = PyTuple_GET_ITEM(item, 1);
	Py_DECREF(item);

https://docs.python.org/3/c-api/tuple.html#c.PyTuple_GetItem

PyObject *PyTuple_GetItem(PyObject *p, Py_ssize_t pos)
...
The returned reference is borrowed from the tuple p (that is: it is only valid as long as you hold a reference to p).
...

PyObject *PyTuple_GET_ITEM(PyObject *p, Py_ssize_t pos)
Return value: Borrowed reference.
Like PyTuple_GetItem(), but does no checking of its arguments.

However, key and value are still used afterwards.

Pillow/src/encode.c

Line 793 in 2c3a977

if (PyDict_GetItemRef(types, key, &tag_type) < 0) {

Pillow/src/encode.c

Line 808 in 2c3a977

if (PyLong_Check(value)) {