Change: Don't change music track when toggling shuffle mode.

[PeterN]

Motivation / Problem

Toggling shuffle mode instantly changes the currently playing music track.

I think it is better for toggling shuffle mode to only affect the playlist order, with no other side effects.

Description

Instead of restarting play back when toggling shuffle, remember the current playlist song and update the playlist position.

Additionally, fix an oversight that meant the playlist window itself is not refreshed when toggling shuffle mode.

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