Fix incorrect method unpacking code in coroutine finalisation code.

Cython/Utility/AsyncGen.c

@@ -223,19 +223,20 @@ __Pyx_async_gen_init_hooks(__pyx_PyAsyncGenObject *o)
     firstiter = tstate->async_gen_firstiter;
     if (firstiter) {
         PyObject *res;
+#if CYTHON_UNPACK_METHODS
+        PyObject *self;
+#endif
 
         Py_INCREF(firstiter);
         // at least asyncio stores methods here => optimise the call
 #if CYTHON_UNPACK_METHODS
-        if (likely(PyMethod_Check(firstiter))) {
-            PyObject *self = PyMethod_GET_SELF(firstiter);
-            if (likely(self)) {
-                PyObject *function = PyMethod_GET_FUNCTION(firstiter);
-                return __Pyx_PyObject_Call2Args(function, self, (PyObject*)o);
-            }
-        }
+        if (likely(PyMethod_Check(firstiter)) && likely((self = PyMethod_GET_SELF(firstiter)) != NULL)) {
+            PyObject *function = PyMethod_GET_FUNCTION(firstiter);
+            res = __Pyx_PyObject_Call2Args(function, self, (PyObject*)o);
+        } else
 #endif
         res = __Pyx_PyObject_CallOneArg(firstiter, (PyObject*)o);
+
         Py_DECREF(firstiter);
         if (unlikely(res == NULL)) {
             return 1;