All numbered tests pass now!

from_cpython/Python/traceback.c

@@ -124,11 +124,14 @@ PyTraceBack_Here(PyFrameObject *frame)
 int
 PyTraceBack_Here_Tb(PyFrameObject *frame, PyTracebackObject** tb)
 {
-    if ((PyObject*)*tb == Py_None) {
-        Py_DECREF(*tb);
+    PyObject* prev_tb = (PyObject*)*tb;
+    if (prev_tb == Py_None) {
+        Py_DECREF(prev_tb);
         *tb = NULL;
+        prev_tb = NULL;
     }
     *tb = newtracebackobject(*tb, frame);
+    Py_XDECREF(prev_tb);
     if (*tb == NULL)
         return -1;
     return 0;