Fix the problem that left-upper side of a moving shape will be flashed. It is because a coord without member always have a {x=0, y=0, w=1, h=1} geometry value. It cause most left-upper corner been updated. It also cause Cairo to update minmum area that include all updated pixels. So, left-upper side of a updated shape will be updated by Cairo by copy application buffer to window. It causes cursor flashing.