Don't fade music out when returning to the menu if it's Presenting VVVVVV

Otherwise, the Presenting VVVVVV for the menu wouldn't play at all.

desktop_version/src/Input.cpp

@@ -2310,7 +2310,9 @@ void mapmenuactionpress()
         //This fixes an apparent frame flicker.
         FillRect(graphics.tempBuffer, 0x000000);
         graphics.fademode = 2;
-        music.fadeout();
+        if (music.currentsong != 6) {
+            music.fadeout();
+        }
         map.nexttowercolour();
         if (!game.glitchrunnermode)
         {