IRIS: Re-add support for stations unknown to T::S::DE::IRIS::Stations

This fixes a regression introduced by 47f76da4

Closes #159

Journeys logged with travelynx v2.8.0 through 2.8.30 are affected by this bug
and will contain incorrect data even after applying this patch – it only
fixes data for new entries.

To Do: See if affected entries can be repaired with a DB migration