Kludge-fix being able to play music in editor

When you're on the music changing screen in the editor, it plays the
current track. When you return, it stops playing the track. However, if
you press escape, it doesn't stop playing the track. This is because
pressing escape just returns to the previous menu without stopping
playing the track.

To fix this, I just added some kludge in the return menu function. This
is kinda super bad but it works for now and is just something to clean
up later. Maybe like each menu having exit callbacks or something, I
dunno.

This is kinda a regression, kinda sorta not. In 2.2 and previous,
pressing escape would just close the settings menu entirely, which also
bypassed the music fadeout. 2.3 made it so pressing escape doesn't
entirely close the settings menu, and just returns to the previous menu,
which fails in a different way. But the intended way is definitely to
select the return option and having the music fade out.

desktop_version/src/Game.cpp

@@ -5838,6 +5838,12 @@ void Game::returnmenu(void)
         return;
     }
 
+    /* FIXME: Super bad kludge, don't hardcode this! */
+    if (currentmenuname == Menu::ed_music)
+    {
+        music.fadeout();
+    }
+
     MenuStackFrame& frame = menustack[menustack.size()-1];
 
     //Store this in case createmenu() removes the stack frame