fix regression caused by #177 in cleaning up
fix regression caused by #177 in cleaning up

The defer of the screen.Fini() needed to include the defer of the
app.wg.Done(), and the original wg.Done needed to be eliminated.
The problem was originally spotted by @thechriswalker, with a proposed
fix that was close but not quite correct.

gdamore/tcell,zyedidia/tcell,zyedidia/tcell,gdamore/tcell