force fancy progressbar redraw on window size change

We always reacted on the size change, but the bar is only redraw if the
precentage changes, which can take quiet a while in big upgrades, so
with a bit of refactoring we can now call for a redraw immediate to fix
this.

This refactor also helps in avoiding obscure pitfalls clangs static
analyser was complaining about (namely failure of ioctl resulting in
garbage values in the struct).