Motivation / Problem

Found a new race condition with ThreadSanitizer, which was really easy to fix.

Description

Otherwise both the draw-thread and game-thread can do it both
at the same time, which gives rather unwanted side-effects.

Calling it from the draw-thread alone is sufficient, as we just
want to create some unpredictable randomness for the player. The
draw-thread is a lot more active (normally) than the game-thread,
so it is the best place of the two to do this.
Additionally, InteractiveRandom() mostly has to do with visuals
that are client-side-only, so more related to drawing than to
game.

That moment you need more words to describe your change than the actual change itself.

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 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