Check Connection availability in NIO loop

Fixes #11

Author: acogoluegnes

src/main/java/com/rabbitmq/client/impl/AMQChannel.java

@@ -143,8 +143,12 @@ public void handleCompleteInboundCommand(AMQCommand command) throws IOException
         if (!processAsync(command)) {
             // The filter decided not to handle/consume the command,
             // so it must be some reply to an earlier RPC.
-            nextOutstandingRpc().handleCommand(command);
-            markRpcFinished();
+            RpcContinuation nextOutstandingRpc = nextOutstandingRpc();
+            // the outstanding RPC can be null when calling Channel#asyncRpc
+            if(nextOutstandingRpc != null) {
+                nextOutstandingRpc.handleCommand(command);
+                markRpcFinished();
+            }
         }
     }
 

src/main/java/com/rabbitmq/client/impl/nio/NioLoop.java

@@ -134,6 +134,11 @@ public void run() {
                                     key.cancel();
                                     continue;
                                 }
+                                if(state.getConnection() == null) {
+                                    // we're in AMQConnection#start, between the header sending and the FrameHandler#initialize
+                                    // let's wait a bit more
+                                    continue;
+                                }
 
                                 DataInputStream inputStream = state.inputStream;