PrintVault Desktop v0.2.18

A fix for the 3D view, worth taking if you picked up 0.2.17.

Opening Send from the viewer and then going back left an empty box where the model had been, and Reset view looked broken from that point on.

Both were the same fault. The viewer draws into a single shared canvas, and restoring a dialog put back an inert copy of it, so the model appeared to vanish and every repaint after that went somewhere off screen. Reset view had been working the whole time, there was just nothing to see.

The bug was not new in 0.2.17, it had simply never come up: any dialog opened on top of the viewer would have done it, and Send is the first one that ever gets opened from in there.