radiobutton: build the new state flags from the previous flags on click

This fixes e.g. sensitivity issues with GtkRadioButton on state update.

https://bugzilla.gnome.org/show_bug.cgi?id=645172

gtk/gtkradiobutton.c

@@ -800,6 +800,8 @@ gtk_radio_button_clicked (GtkButton *button)
 
   g_object_ref (GTK_WIDGET (button));
 
+  new_state = gtk_widget_get_state_flags (GTK_WIDGET (button));
+
   if (gtk_toggle_button_get_active (toggle_button))
     {
       tmp_button = NULL;