refactor(query):check for none table.

source/dnode/vnode/src/tsdb/tsdbRead.c

@@ -3507,6 +3507,7 @@ int32_t tsdbReaderOpen(SVnode* pVnode, SQueryTableDataCond* pCond, SArray* pTabl
     goto _err;
   }
 
+  if (numOfTables > 0) {
     code = tsdbTakeReadSnap(pReader->pTsdb, &pReader->pReadSnap);
     if (code != TSDB_CODE_SUCCESS) {
       goto _err;
@@ -3549,6 +3550,7 @@ int32_t tsdbReaderOpen(SVnode* pVnode, SQueryTableDataCond* pCond, SArray* pTabl
         }
       }
     }
+  }
 
   tsdbDebug("%p total numOfTable:%d in this query %s", pReader, numOfTables, pReader->idStr);
   return code;
@@ -3604,6 +3606,10 @@ void tsdbReaderClose(STsdbReader* pReader) {
     taosMemoryFree(pLReader);
   }
 
+  if (pReader->innerReader[0] != 0) {
+    tsdbUntakeReadSnap(pReader->innerReader[0]->pTsdb, pReader->innerReader[0]->pReadSnap);
+  }
+
   tsdbDebug(
       "%p :io-cost summary: head-file:%" PRIu64 ", head-file time:%.2f ms, SMA:%" PRId64
       " SMA-time:%.2f ms, fileBlocks:%" PRId64 ", fileBlocks-load-time:%.2f ms, "