Use ConnectAsync before Subscribe does not subscribe correctly

[maordavidov]

The following won't work:

await MQTTService.client.ConnectAsync();
MQTTService.observableMessage.Subscribe(new MQTTObserver());

While this one will:

MQTTService.observableMessage.Subscribe(new MQTTObserver());
await MQTTService.client.ConnectAsync();