ico: Fix area-updated coordinates
ico: Fix area-updated coordinates

When the icon is constructed bottom to top, the y coordinates were
incorrectly computed.

https://bugzilla.gnome.org/show_bug.cgi?id=581484

GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf