eval_code2(): In the extended calling syntax opcodes, you must check

the return value of PySequence_Length().  If an exception occurred,
the returned length will be -1.  Make sure this doesn't get obscurred,
and that the bogus length isn't used.

Python/ceval.c

@@ -1636,6 +1636,14 @@ eval_code2(co, globals, locals,
 				break;
 			    }
 			    nstar = PySequence_Length(stararg);
+			    if (nstar < 0) {
+				    if (!PyErr_Occurred)
+					    PyErr_SetString(
+						    PyExc_TypeError,
+						    "len() of unsized object");
+				    x = NULL;
+				    break;
+			    }
 			}
 			if (nk > 0) {
 			    if (kwdict == NULL) {