Don't allow websocket close to prevent lingering print jobs

[tresf]

It's fairly common for users to navigate away from a page before the print job has been processed. Although this is not ideal, the currently behavior is sporadic, depending on where in the print process it was.

@bberenz is there a way to let the jobs print even after the websocket has been disconnected? Currently, I believe the entire job fails if the timing is wrong.