Don't allow setting best game deaths in custom levels

Custom levels shouldn't touch main game save data, and best game deaths
is no exception.

I also added a MAKEANDPLAY ifdef just to be safe.

desktop_version/src/Game.cpp

@@ -2672,6 +2672,9 @@ void Game::updatestate(void)
                 unlocknum(19);
             }
 
+#ifndef MAKEANDPLAY
+            if (!map.custommode)
+            {
                 if (bestgamedeaths == -1)
                 {
                     bestgamedeaths = deathcounts;
@@ -2683,6 +2686,8 @@ void Game::updatestate(void)
                         bestgamedeaths = deathcounts;
                     }
                 }
+            }
+#endif
 
             if (bestgamedeaths > -1) {
                 if (bestgamedeaths <= 500) {