LinGui: fix gtk3 subtitle and audio list issue

The wrong subtitle or audio track was sometimes getting removed from the
list when the remove button was pressed.

The sequence of widget callbacks changed is such a way as to require some
small rearrangement of code.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5222 b64f7644-9d1e-0410-96f1-a4d463321fa5