Motivation / Problem

See #8123. When a tram is on a half-tile, it cannot find any depot until it leaves the tile.

Description

Basically, follow_track.hpp contains a fix for half-tiles, but
this wasn't duplicated for when trying to find a depot and in
a few other places. This makes sure all places act the same.

Because TrackBits don't know the concept of half-tiles, there is a hack in place that if GetTileTrackStatus returns zero, it checks if the tile has a single bit of tram tracks. In that case, it acts like it is a tram track going on either the X or Y axis. in follow_track.hpp there is code preventing the pathfinder from exiting the tile on the wrong side in these cases, "fixing" the path finder in believing it is a half-tile.

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.

Limitations

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.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker