Change: Try stopping extmidi player with SIGINT first.

[PeterN]

Motivation / Problem

On Linux with extmidi music playback, stopping playback or switching to the next track may leave stuck notes. This is because it's down to the external player to turn those notes off, and we kill the process with SIGTERM which can interrupt this.

Description

Instead, try sending SIGINT first, and if that fails fall back to SIGTERM then SIGKILL. This can give the player a chance to issue MIDI note-off commands.

This fixes at least pmidi leaving stuck notes on.

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