Fade out music at end of level, before intermission

Small polish feature to fade out the level music before intermission, like Sonic 3.

Test cases, please break:

• Single player
• Splitscreen: Co-op with playersforexit One (one player needed to exit the level)
• Splitscreen: Co-op with playersforexit All (all players needed to exit the level)
• Splitscreen: Race when all players finish (exits immediately, no fade)
• Splitscreen: Race when player finishes during the countdown (exits immediately, no fade)
• Splitscreen: Race when player does not reach the end (countdown music finishes, does not fade)
• Splitscreen: Ringslinger (does not fade at end of level; should we support this? I'm thinking no.)
• Netgame, for all the above
• Headless server (render_mode is none)
• Anything else?

musicplus-endoflevel

changed the description

added 1 commit

• f18103a4 - Declare exitfadestarted properly

Compare with previous version

Test EXE, 32-bit: https://ci.appveyor.com/api/buildjobs/25c78mok7v5gj6iy/artifacts/public-musicplus-feature-endoflevel-SDL.7z

Test EXE, 64-bit: https://ci.appveyor.com/api/buildjobs/ar9kr0a7tebke17y/artifacts/public-musicplus-feature-endoflevel-SDL64.7z

resolved all discussions

Everything works as it should

merged

mentioned in commit 47eb7110