The patch was causing a failure in test_codeccallbacks, issue8271v4 fixes the test.
(The failing test in test_codeccallbacks was testing that registering error handlers works, using a function that replaced "\xc0\x80" with "\x00". Since now "\xc0" is an invalid start byte regardless of what follows, the function is now receiving only "\xc0" instead of "\xc0\x80" so I had to change the test.)