Update Diverter to return existing Redirects from its RedirectSet

[devodo]

Previously a Diverter instance only allowed retrieval of Redirects. If an attempt was made to retrieve an unregistered Redirect a DiverterException was thrown.

This update is to extend a Diverter instance to also be able to retrieve any existing Redirect from its RedirectSet. So, for example, if a Redirect has been inserted into the RedirectSet from a ViaRedirect this allows it to be retrieved directly from the Diverter instance.