Fix a race when client isn't ready yet to receive messages
Fix a race when client isn't ready yet to receive messages

When 2 messages are coming close from one to another, the writer isn't ready
yet to process it, and so, we go back to the default case sending a message
on error.
Dismiss that, we detect websocket disconnection by another mean anyway and go
back to pure synchronicity.

ubuntu/booth-demo-manager,ubuntu/booth-demo-manager,ubuntu/booth-demo-manager,ubuntu/booth-demo-manager