Motivation / Problem

Crash when closing airport hangar window

Description

Airport hangars are weird, they don't use the DepotID that everything else uses. #8717 did not account for this.
Generalise usages of this into a small function to help prevent it from happening again.

Limitations

None.
Could be some issues with functions casting between StationID/DepotID/uint16. Check CI for new compiler warnings.

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