check for closing rather than broker initiated closing

Author: Alexandru Scvortov

src/com/rabbitmq/client/impl/AMQConnection.java

@@ -530,7 +530,7 @@ public boolean processControlCommand(Command c)
         Method method = c.getMethod();
 
         if (method instanceof AMQP.Connection.Close) {
-            if (!_brokerInitiatedShutdown) {
+            if (!isOpen()) {
                 handleConnectionClose(c);
             } else {
                 // Already shutting down, so just send back a CloseOk.