修复mysql中数据为NULL的时候，查询字段被丢弃的bug。
修复mysql中数据为NULL的时候，查询字段被丢弃的bug。

swoole/swoole-src,LinkedDestiny/swoole-src,LinkedDestiny/swoole-src,AJSoft/swoole-src,tutanhamon/swoole-src,LinkedDestiny/swoole-src,swoole/swoole-src,swoole/swoole-src,swoole/swoole-src,tutanhamon/swoole-src,AJSoft/swoole-src,swoole/swoole-src,AJSoft/swoole-src,LinkedDestiny/swoole-src,AJSoft/swoole-src,swoole/swoole-src,AJSoft/swoole-src,AJSoft/swoole-src,tutanhamon/swoole-src,LinkedDestiny/swoole-src,tutanhamon/swoole-src,swoole/swoole-src,LinkedDestiny/swoole-src,tutanhamon/swoole-src,AJSoft/swoole-src,tutanhamon/swoole-src,tutanhamon/swoole-src,LinkedDestiny/swoole-src