LinGui: fix range update issues and plug memory leaks

Updating the range of GtkScale and GtkSpinButtons causes the current
value to update inappropriately under some conditions.  So update
the range and value concurrently.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6051 b64f7644-9d1e-0410-96f1-a4d463321fa5