Fixes OOIION-590 (Fixes UNS regarding emails being sent to events not subscribed to)

The UNS utility method designed to figure out interested users was not properly handling the case of events coming from the same origin and whose event subtypes and origin_type fields were empty.

This pull request patches the method so that it properly handles all cases.

It has been verified that only emails for the event subscribed to is being sent now.