fix:core dump if data block size is 0

source/dnode/vnode/src/tq/tqExec.c

@@ -152,7 +152,7 @@ int32_t tqScanTaosx(STQ* pTq, const STqHandle* pHandle, STaosxRsp* pRsp, SMqMeta
     }
     tqDebug("tmqsnap task execute end, get %p", pDataBlock);
 
-    if (pDataBlock != NULL) {
+    if (pDataBlock != NULL && pDataBlock->info.rows > 0) {
       if (pRsp->withTbName) {
         int64_t uid = 0;
         if (pOffset->type == TMQ_OFFSET__LOG) {

tests/system-test/7-tmq/subscribeDb4.py

@@ -26,7 +26,7 @@ class TDTestCase:
                 'ctbPrefix':  'ctb',
                 'ctbStartIdx': 0,
                 'ctbNum':     10,
-                'rowsPerTbl': 10000,
+                'rowsPerTbl': 50000,
                 'batchNum':   10,
                 'startTs':    1640966400000,  # 2022-01-01 00:00:00.000
                 'pollDelay':  20,