mesh gen progress stack overflow

[Optiligence]

https://github.com/knossos-project/knossos/blob/0baebe43530845be1e1683b98318d4c53caeaccf/mesh/mesh_generation.cpp#L217 When a lot of signals accumulate asynchronously in the event queue, QApplication::processEvents() in QProgressDialog::setValue results in a stack overflow.