[td-225]fix bug found by crash_gen

src/client/src/tscSubquery.c

@@ -667,7 +667,6 @@ static int32_t tscLaunchRealSubqueries(SSqlObj* pSql) {
       continue;
     }
 
-//    tscDoQuery(pSql->pSubs[i]);
     SQueryInfo* pQueryInfo = tscGetQueryInfo(&pSql->pSubs[i]->cmd, 0);
     executeQuery(pSql->pSubs[i], pQueryInfo);
   }

src/client/src/tscUtil.c

@@ -2783,6 +2783,11 @@ void doExecuteQuery(SSqlObj* pSql, SQueryInfo* pQueryInfo) {
 
 // do execute the query according to the query execution plan
 void executeQuery(SSqlObj* pSql, SQueryInfo* pQueryInfo) {
+  if (pSql->cmd.command == TSDB_SQL_RETRIEVE_EMPTY_RESULT) {
+    (*pSql->fp)(pSql->param, pSql, 0);
+    return;
+  }
+
   if (taosArrayGetSize(pQueryInfo->pUpstream) > 0) {  // nest query. do execute it firstly
     SQueryInfo* pq = taosArrayGetP(pQueryInfo->pUpstream, 0);