fix(query): add null ptr check when retrieving the block info.

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

@@ -4398,7 +4398,7 @@ int64_t tsdbGetNumOfRowsInMemTable(STsdbReader* pReader) {
     STableBlockScanInfo* pBlockScanInfo = *(STableBlockScanInfo**)pStatus->pTableIter;
 
     STbData* d = NULL;
-    if (pReader->pTsdb->mem != NULL) {
+    if (pReader->pReadSnap->pMem != NULL) {
       d = tsdbGetTbDataFromMemTable(pReader->pReadSnap->pMem, pReader->suid, pBlockScanInfo->uid);
       if (d != NULL) {
         rows += tsdbGetNRowsInTbData(d);
@@ -4406,7 +4406,7 @@ int64_t tsdbGetNumOfRowsInMemTable(STsdbReader* pReader) {
     }
 
     STbData* di = NULL;
-    if (pReader->pTsdb->imem != NULL) {
+    if (pReader->pReadSnap->pIMem != NULL) {
       di = tsdbGetTbDataFromMemTable(pReader->pReadSnap->pIMem, pReader->suid, pBlockScanInfo->uid);
       if (di != NULL) {
         rows += tsdbGetNRowsInTbData(di);