Redraw the window after an expose event

Expose events, according to the X11 documentation, signify when the
contents of a window region have been lost but until now we have been
ignoring this event for unknown reasons.

Handle this event by redrawing the window entirely. While this is not a
perfect solution, the optimal one would be to only redraw the
region that was lost, it's simpler to implement currently and better
than losing the contents of the window entirely.

src/x11/x.c

@@ -814,6 +814,7 @@ gboolean x_mainloop_fd_dispatch(GSource * source, GSourceFunc callback,
                 switch (ev.type) {
                 case Expose:
                         if (ev.xexpose.count == 0 && xctx.visible) {
+                                x_win_draw();
                         }
                         break;
                 case SelectionNotify: