Simplify C helper code.

Cython/Utility/ObjectHandling.c

@@ -276,10 +276,15 @@ static CYTHON_INLINE PyObject *__Pyx_PyObject_GetItem(PyObject *obj, PyObject* k
 
 #if CYTHON_USE_TYPE_SLOTS
 static PyObject *__Pyx_PyObject_GetIndex(PyObject *obj, PyObject* index) {
-    PySequenceMethods *m = Py_TYPE(obj)->tp_as_sequence;
-    if (likely(m && m->sq_item)) {
     PyObject *runerr;
-        Py_ssize_t key_value = __Pyx_PyIndex_AsSsize_t(index);
+    Py_ssize_t key_value;
+    PySequenceMethods *m = Py_TYPE(obj)->tp_as_sequence;
+    if (unlikely(!(m && m->sq_item))) {
+        PyErr_Format(PyExc_TypeError, "'%.200s' object is not subscriptable", Py_TYPE(obj)->tp_name);
+        return NULL;
+    }
+
+    key_value = __Pyx_PyIndex_AsSsize_t(index);
     if (likely(key_value != -1 || !(runerr = PyErr_Occurred()))) {
         return __Pyx_GetItemInt_Fast(obj, key_value, 0, 1, 1);
     }
@@ -289,9 +294,6 @@ static PyObject *__Pyx_PyObject_GetIndex(PyObject *obj, PyObject* index) {
         PyErr_Clear();
         PyErr_Format(PyExc_IndexError, "cannot fit '%.200s' into an index-sized integer", Py_TYPE(index)->tp_name);
     }
-    } else {
-        PyErr_Format(PyExc_TypeError, "'%.200s' object is not subscriptable", Py_TYPE(obj)->tp_name);
-    }
     return NULL;
 }