Fix bug: Playing music during Game Over screen

This fixes a long-standing bug where it's possible to play music during
the Game Over screen in No Death Mode. All you have to do is die while
music is fading out from one area to the next.

The easiest way to do this is in the entrance to Space Station 2, since
there's a music change to Passion for Exploring in Outer Hull (you will
need to go into the zone far enough to activate Pushing Onwards first),
which also contains spikes to die on.

Basically, it's a simple oversight because the nicefade system relies on
music fading out to start playing the next track, but in this case, No
Death Mode fades the music out without accounting for that. It's best to
just disable nicefade entirely when dying in No Death Mode.

Thanks to KSS for reporting this bug.

desktop_version/src/Game.cpp

@@ -5029,6 +5029,9 @@ void Game::deathsequence(void)
         {
             music.fadeout();
             gameoverdelay = 60;
+
+            /* Fix a bug being able to play music on the Game Over screen */
+            music.nicefade = false;
         }
         deathcounts++;
         music.playef(2);