Some sites do not use postponed_date at all.
It would be a massive performance issue to still search for them for
each and every date instance that is created.
This small addition will solve the issue for those pages.
It will still once at least one internal reference is added.
We could then try to add proxies which are build and added, but don't
use the DB. That way the performance would still be okay, and data will
only be fetched when used.
