[cocos2d-lua] crash崩溃了几十次

堆栈信息如下：
```
...Bin/trunk/client/cocos/src/app/poco/poco_manager.lua:111: attempt to index local 'client_sock' (a nil value)
.../trunk/client/cocos/src/main.lua:23: in function <...ace/trunk/client/cocos/src/main.lua:16>
...Bin/trunk/client/cocos/src/app/poco/poco_manager.lua:111: in function 'server_loop'
...Bin/trunk/client/cocos/src/app/poco/poco_manager.lua:96: in function <...Bin/trunk/client/cocos/src/app/poco/poco_manager.lua:96>
```
昨天做了多台机子测试，共出现了几十次这个堆栈错误告警

sdk版本：cocos2d-lua poco sdk(v1.0.6_2018-5-15)