special case Py_None in __Pyx_PyObject_IsTrue()

Cython/Compiler/PyrexTypes.py

@@ -1399,6 +1399,7 @@ static INLINE Py_ssize_t __pyx_PyIndex_AsSsize_t(PyObject* b) {
 static INLINE int __Pyx_PyObject_IsTrue(PyObject* x) {
    if (x == Py_True) return 1;
    else if (x == Py_False) return 0;
+   else if (x == Py_None) return 0;
    else return PyObject_IsTrue(x);
 }