add more check

src/query/src/qExecutor.c

@@ -5517,8 +5517,10 @@ static SSDataBlock* doSort(void* param, bool* newgroup) {
   }
 
   __compar_fn_t  comp = getKeyComparFunc(pSchema[pInfo->colIndex].type, pInfo->order);
-  taoscQSort(pCols, pSchema, numOfCols, pInfo->pDataBlock->info.rows, pInfo->colIndex, comp);
-
+  if (pInfo->pDataBlock->info.rows) {
+    taoscQSort(pCols, pSchema, numOfCols, pInfo->pDataBlock->info.rows, pInfo->colIndex, comp);
+  }
+  
   tfree(pCols);
   tfree(pSchema);
   return (pInfo->pDataBlock->info.rows > 0)? pInfo->pDataBlock:NULL;