[data ingestion] handle termination in worker pool (#19192)

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- [ ] Protocol:
- [ ] Nodes (Validators and Full nodes):
- [ ] Indexer:
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crates/sui-data-ingestion-core/src/worker_pool.rs

@@ -123,7 +123,11 @@ impl<W: Worker + 'static> WorkerPool<W> {
                         }
                     }
                 }
-                Some(checkpoint) = checkpoint_receiver.recv() => {
+                maybe_checkpoint = checkpoint_receiver.recv() => {
+                    if maybe_checkpoint.is_none() {
+                        break;
+                    }
+                    let checkpoint = maybe_checkpoint.expect("invariant's checked");
                     let sequence_number = checkpoint.checkpoint_summary.sequence_number;
                     if sequence_number < current_checkpoint_number {
                         continue;