fix the problem that the reference of serverHook in Plugin object is null

src/main/java/emu/grasscutter/Grasscutter.java

@@ -92,14 +92,13 @@ public final class Grasscutter {
 		// Database
 		DatabaseManager.initialize();
 
-		// Create plugin manager instance.
-		pluginManager = new PluginManager();
-
 		// Create server instances.
 		dispatchServer = new DispatchServer();
 		gameServer = new GameServer(new InetSocketAddress(getConfig().getGameServerOptions().Ip, getConfig().getGameServerOptions().Port));
 		// Create a server hook instance with both servers.
 		new ServerHook(gameServer, dispatchServer);
+		// Create plugin manager instance.
+		pluginManager = new PluginManager();
 
 		// Start servers.
 		if (getConfig().RunMode == ServerRunMode.HYBRID) {

src/main/java/emu/grasscutter/server/game/GameServer.java

@@ -28,6 +28,9 @@ import java.net.InetSocketAddress;
 import java.time.OffsetDateTime;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
 
 public final class GameServer extends KcpServer {
 	private final InetSocketAddress address;
@@ -68,19 +71,6 @@ public final class GameServer extends KcpServer {
 		this.dropManager = new DropManager(this);
 		this.combineManger = new CombineManger(this);
 		
-		// Schedule game loop.
-		Timer gameLoop = new Timer();
-		gameLoop.scheduleAtFixedRate(new TimerTask() {
-			@Override
-			public void run() {
-				try {
-					onTick();
-				} catch (Exception e) {
-					Grasscutter.getLogger().error(Grasscutter.getLanguage().An_error_occurred_during_game_update, e);
-				}
-			}
-		}, new Date(), 1000L);
-		
 		// Hook into shutdown event.
 		Runtime.getRuntime().addShutdownHook(new Thread(this::onServerShutdown));
 	}
@@ -212,6 +202,23 @@ public final class GameServer extends KcpServer {
 		
 	}
 
+	@Override
+	public synchronized void start() {
+		// Schedule game loop.
+		ScheduledExecutorService gameLoop = Executors.newScheduledThreadPool(2);
+		gameLoop.scheduleAtFixedRate(new TimerTask() {
+			@Override
+			public void run() {
+				try {
+					onTick();
+				} catch (Exception e) {
+					Grasscutter.getLogger().error(Grasscutter.getLanguage().An_error_occurred_during_game_update, e);
+				}
+			}
+		}, 0L, 1000L, TimeUnit.MILLISECONDS);
+		super.start();
+	}
+
 	@Override
 	public void onStartFinish() {
 		Grasscutter.getLogger().info(Grasscutter.getLanguage().Grasscutter_is_free);