GUI shouldn't gray out when device auto-powers down

[jgoerzen]

Hi,

Thanks again for Labelle!

My LabelManager 280 has some sort of a self-powerdown timer. It will shut itself off after a few minutes. I imagine the GUI is reading some data about the printer when it starts, but it is somewhat annoying to have it shut down mid-edit when the printer turns itself off. If it could stay enabled, that would be great.