* [TD-13708]<test>:csharp connector subscribe test cases

* [TD-13708]<test>:fix indent

* [TD-13708]<test>:fix with comment

* [TD-13708]<test>:fix error info and uncomment database fixture dispose method

* [TD-13708]<test>:fix error info

* [TD-13708]<test>:fix error info,taos_errstr work for null point