Fix htrc metadata workset path parsing

[JaimieMurdock]

Each one of these commands should not return null, but rather the actual metadata for the items. They are the examples from the documentation.

jaimie@compy386:/tmp$ htrc metadata 001423370
{"001423370": null}

jaimie@compy386:/tmp$ htrc metadata "https://babel.hathitrust.org/cgi/pt?id=mdp.39015078560078;view=1up;seq=13"
ERROR:root:No result found for https://babel.hathitrust.org/cgi/pt?id=mdp.39015078560078;view=1up;seq=13
{"https://babel.hathitrust.org/cgi/pt?id=mdp.39015078560078;view=1up;seq=13": {}}

jaimie@compy386:/tmp$ htrc metadata "https://catalog.hathitrust.org/Record/001423370"
{"https://catalog.hathitrust.org/Record/001423370": null}