Fix multiple audio bug when exiting gameplay

Author: zulsinar031

source/core/src/main/com/csse3200/game/GdxGame.java

@@ -23,6 +23,7 @@
  */
 public class GdxGame extends Game {
   private static final Logger logger = LoggerFactory.getLogger(GdxGame.class);
+  public static int musicON = 0;
 
   @Override
   public void create() {

source/core/src/main/com/csse3200/game/screens/MainMenuScreen.java

@@ -105,8 +105,12 @@ private void registerAudioAssets() {
   }
 
   private void playMenuMusic() {
-    if (ServiceLocator.getAudioService() != null) {
-      ServiceLocator.getAudioService().playMusic("menu_bgm", true);
+    if (GdxGame.musicON == 0) {
+      if (ServiceLocator.getAudioService() != null) {
+        ServiceLocator.getAudioService().playMusic("menu_bgm", true);
+        // Set the flag to indicate music is now on
+        GdxGame.musicON = 1;
+      }
     }
   }