Waiting for ack

I'm trying to consume 1 message at a time, and i'm acknowledging the message outside of the listener. But it's just grabbing the next message without waiting for the ack.

code sample:
```js
let msg;
let msgConsumer;

const consumer = client.subscribe({
topic: `persistent://public/default/test1`,
subscription: `sub1`,
subscriptionType: 'Exclusive',
receiverQueueSize:0,
ackTimeoutMs:300000,
listener: (msg,msgConsumer) => {
console.log(msg.getData().toString());
msg = msg;
msgConsumer = msgConsumer;

}
});

function someWhereElse(){

msgConsumer.acknowledge(msg);

}
```
Is something like this possible?

Start at the NodeJS client's subscribe listener and acknowledgement flow shown in the example, checking how receiverQueueSize: 0 and acknowledgements made outside the listener are handled. Reproduce the subscription with one message in flight and determine whether the next message arrives before acknowledge(msg); done means the sequencing is corrected or the supported behavior is documented.

Written by the indexing model from the issue text.