Add new port preference availability check to Printer Manager modal.

[NotExpectedYet]

Description of the problem

Currently it's only the settings that check for the port preference availability. This check needs adding into the Printer Manager Modal too.

I believe it would also be beneficial to disable the connect button, as that's going to fail anyway we might as well not allow it.

Reproduction of the problem

Open Printer Settings with printer offline (not in port list), see the new check.
Open Printer Manager with printer offline (not in port list), aww no check!