[PATCH] Small Gtk font dialog fix

Hi,

Fixed a small problem in the Font dialog where when a formatting option
(strike/underline/overline) is set, and the user tries to unset them
using the toggle button, nothing happens. This is due to the "toggled"
signal handler being called twice, once as result of
gtk_toggle_button_set_active(,true) and second time the user clicks the
button.