Unexpected change in behaviour when short dates are used

[anjackson]

The test suite uses test URLs like https://www.webarchive.org.uk/wayback/en/archive/2018/https://www.bl.uk/ and expects the 2018 to get expanded to the closest date. This certainly worked, at least until recently.

Now, short date strings eventually get

                    Internal Error: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))

(possibly from the CDX server somehow?!)