完成离线消息发送和上线获取离线消息

Hotfix/Chat/Handler/C2Chat_JoinChannelRequestHandler.cs

@@ -13,6 +13,11 @@ public class
     protected override async FTask Run(ChatUnit entity, C2Chat_JoinChannelRequest request,
         Caht2C_JoinChannelResponse response, Action reply)
     {
+        if (request.Target < 1)
+        {
+            response.ErrorCode = ErrorCode.ErrArgs;
+            return;
+        }
         var channelCenter = entity.Scene.GetComponent<ChatChannelCenterComponent>();
         if (channelCenter == null)
         {