Fix #9642: Keep infrastructure totals when overbuilding road depots.

[J0anJosep]

Motivation / Problem

If you overbuild a road depot, the company road infrastructure details are wrong, as each time you overbuild it, 2 more trackbits are added to the company totals.

As after loading a game those stats are recomputed, the problem didn't arise sooner and old savegames don't need to be modified to fix the bug.

Description

This PR fixes the incorrect behaviour: overbuilding a road depot doesn't add or remove to company road infrastructure totals.

Limitations

None?

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