Fixed NPE on ServerListPing if plugin isn't fully started / arenaregistry not ready

Author: Tigerpanzer02

MiniGamesBox Classic/src/main/java/plugily/projects/minigamesbox/classic/arena/managers/BungeeManager.java

@@ -76,6 +76,10 @@ public void connectToHub(Player player) {
 
   @EventHandler(priority = EventPriority.HIGHEST)
   public void onServerListPing(ServerListPingEvent event) {
+    if(plugin.getArenaRegistry() == null) {
+      //can be null on early request after server startup
+      return;
+    }
     if(plugin.getArenaRegistry().getArenas().isEmpty() || !config.getBoolean("MOTD.Manager")) {
       return;
     }