Fix #8123: trams on half-tiles couldn't find depots #8738
Motivation / Problem
See #8123. When a tram is on a half-tile, it cannot find any depot until it leaves the tile.
Because TrackBits don't know the concept of half-tiles, there is a hack in place that if
This worked well for normal cases, but when clicking "Goto Depot" while on a half-tile, it aborted early thinking there was no way to find a way off its current tile. There were several other cases where the source tile could be empty because it didn't carry over this fix.
I am touching the pathfinder. Who knows what the side-effects are.
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.
I added some more words in the