[#1568] rocketmq need enhance stability when commitlog broken

 增加非空判断，防止空指针异常,导致循环事务 check,增加test覆盖

broker/src/main/java/org/apache/rocketmq/broker/transaction/queue/TransactionalMessageBridge.java

@@ -131,6 +131,9 @@ public class TransactionalMessageBridge {
                     this.brokerController.getBrokerStatsManager().incGroupGetSize(group, topic,
                         getMessageResult.getBufferTotalSize());
                     this.brokerController.getBrokerStatsManager().incBrokerGetNums(getMessageResult.getMessageCount());
+                    if ( foundList == null || foundList.size() == 0 ) {
+                        break;
+                    }
                     this.brokerController.getBrokerStatsManager().recordDiskFallBehindTime(group, topic, queueId,
                         this.brokerController.getMessageStore().now() - foundList.get(foundList.size() - 1)
                             .getStoreTimestamp());

broker/src/test/java/org/apache/rocketmq/broker/transaction/queue/TransactionalMessageBridgeTest.java

@@ -167,6 +167,24 @@ public class TransactionalMessageBridgeTest {
         assertThat(messageExt).isNotNull();
     }
 
+    @Test
+    public void testGetHalfMessageStatusFound() {
+        when(messageStore
+                .getMessage(anyString(), anyString(), anyInt(), anyLong(), anyInt(), ArgumentMatchers.nullable(MessageFilter.class)))
+                .thenReturn(createGetMessageResult(GetMessageStatus.FOUND));
+        PullResult result = transactionBridge.getHalfMessage(0, 0, 1);
+        assertThat(result.getPullStatus()).isEqualTo(PullStatus.FOUND);
+    }
+
+    @Test
+    public void testGetHalfMessageNull() {
+        when(messageStore
+                .getMessage(anyString(), anyString(), anyInt(), anyLong(), anyInt(), ArgumentMatchers.nullable(MessageFilter.class)))
+                .thenReturn(null);
+        PullResult result = transactionBridge.getHalfMessage(0, 0, 1);
+        assertThat(result.getPullStatus()).isNull();
+    }
+
     private GetMessageResult createGetMessageResult(GetMessageStatus status) {
         GetMessageResult getMessageResult = new GetMessageResult();
         getMessageResult.setStatus(status);