Fix resizing the window smaller.

Fix resizing the window smaller.

Some weird sequence of events was triggering an attempted redraw at
the old size, before properly noticing the change and redrawing at the
new size. When going from smaller to bigger this just caused a display
flicker (in fact not even a perceptible one), but bigger to smaller
caused an exception when we tried to draw a big screen in a small
window and curses caught us printing outside the screen area.

Now seems to work better.