Pipe: Fixed the NPE of progress report event (#17474)

Author: Caideyipi

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/source/dataregion/realtime/PipeRealtimeDataRegionSource.java

@@ -431,7 +431,11 @@ protected void extractProgressReportEvent(final PipeRealtimeEvent event) {
     // Since the batch and retry queue no longer need the heartbeat event to trigger
     // And the progress report event can trigger the processor calculation because it's not reported
     // yet
-    while (((PipeRealtimeEvent) pendingQueue.peekLast()).getEvent() instanceof PipeHeartbeatEvent) {
+    while (true) {
+      final PipeRealtimeEvent lastEvent = ((PipeRealtimeEvent) pendingQueue.peekLast());
+      if (lastEvent == null || !(lastEvent.getEvent() instanceof PipeHeartbeatEvent)) {
+        break;
+      }
       pendingQueue.pollLast();
     }
     if (pendingQueue.peekLast() instanceof ProgressReportEvent) {