[cjson] precautions for root node

1. problem ： Writing loadruner Script time , Frequently perform a test on a data cJSON_Parse after , Call again cJSON_Delete After release , It will cause sudden interruption of concurrent users , Report errors ; Analysis error later , Found to be cJSON_Delete Abnormal exit

2. resolvent ： Do not operate data frequently , Try to return data for one , It can be handled once , Avoid this anomaly .

3. Code ：