LinGui: work around bug in GtkScaleButton
When the button value is updated programatically, the update event is not
sent and therefore the label is not updated.  So update the label manually
instead of relying on the event to trigger the update.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6230 b64f7644-9d1e-0410-96f1-a4d463321fa5