stop partitionOffsetChan if closed

weed/mq/client/sub_client/on_each_partition.go

@@ -67,6 +67,11 @@ func (sub *TopicSubscriber) onEachPartition(assigned *mq_pb.BrokerPartitionAssig
 					subscribeClient.CloseSend()
 					return
 				case ack := <-partitionOffsetChan:
+				case ack, ok := <-partitionOffsetChan:
+					if !ok {
+						subscribeClient.CloseSend()
+						return
+					}
 					subscribeClient.SendMsg(&mq_pb.SubscribeMessageRequest{
 						Message: &mq_pb.SubscribeMessageRequest_Ack{
 							Ack: &mq_pb.SubscribeMessageRequest_AckMessage{