Fix: AirportGetNearestTown incorrectly assumed first TileIterator result was origin.

[PeterN]

Motivation / Problem

AirportGetNearestTown uses the first result of TileIterator and assumes it is the origin tile. However not all TileIterators are equal, and some do not start at the top-corner, so the perimeter check was wrong.

AirportTileTableIterator iterates the tiles in the airport spec, which is made up from a list of offsets. These can start anywhere within the layout.

As the perimeter is used to limit the range of tiles that are checked, if it is wrong then some tiles will be missed, which can result in the wrong town being returned. This then leads on to station noise level being applied/removed from the wrong town.

Description

As the caller already has the origin tile, pass that and use it to determine the perimeter instead.

This issue was found by asserting that TileX(cur_tile) and TileY(cur_tile) were within the perimeter bounds.

Limitations

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 touches english.txt or translations? Check the guidelines
• 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, game_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