Avoid AlreadyClosedException where we can

Author: michaelklishin

projects/client/RabbitMQ.Client/src/client/messagepatterns/Subscription.cs

@@ -157,7 +157,11 @@ public void Close()
                 }
 
                 if (shouldCancelConsumer) {
-                    m_model.BasicCancel(m_consumerTag);
+                    if(m_model.IsOpen)
+                    {
+                        m_model.BasicCancel(m_consumerTag);
+                    }
+                    
                     m_consumerTag = null;
                 }
             } catch (OperationInterruptedException) {
@@ -190,7 +194,7 @@ public void Ack(BasicDeliverEventArgs evt)
 
             lock(m_eventLock)
             {
-                if (!m_noAck) {
+                if (!m_noAck && m_model.IsOpen) {
                     m_model.BasicAck(evt.DeliveryTag, false);
                 }
 
@@ -236,7 +240,7 @@ public void Nack(BasicDeliverEventArgs evt,
 
             lock(m_eventLock)
             {
-                if (!m_noAck) {
+                if (!m_noAck && m_model.IsOpen) {
                     m_model.BasicNack(evt.DeliveryTag, multiple, requeue);
                 }