修复消息bug

modules/users/models/user_message_model.js

@@ -35,7 +35,7 @@ class UserMessageModel extends BaseModel {
         let option = {pageSize: 1, offset: 0};
         option.sort = {create_time: -1};
         let lastMessageData = await this.db.find({user_id: userId}, null, option);
-        lastMessageData = lastMessageData === null ? null : lastMessageData[0];
+        lastMessageData = lastMessageData === null || lastMessageData.length <= 0 ? null : lastMessageData[0];
         let lastTime = lastMessageData === null ? 0 : lastMessageData.create_time;
 
         // 查找已发布的数据