[Dataflow Streaming] Fix spammy log during GrpcGetDataStream physical stream half-closing (#38158)

Author: scwhittle

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/GrpcGetDataStream.java

@@ -226,12 +226,15 @@ public void onResponse(StreamingGetDataResponse chunk) {
 
     @Override
     public boolean hasPendingRequests() {
+      // Note the batchesSizeSupplier may reflect batches that could be sent on another physical
+      // stream. However we treat them as possibly pending on all physical streams to ensure that we
+      // recreate streams to send them.
       return !pending.isEmpty() || batchesSizeSupplier.get() > 0;
     }
 
     @Override
     public void onDone(Status status) {
-      if (status.isOk() && hasPendingRequests()) {
+      if (status.isOk() && !pending.isEmpty()) {
         LOG.warn("Pending requests not expected on successful GetData stream flushing.");
       }
       for (AppendableInputStream responseStream : pending.values()) {