libhb: fix a problem with BD audio track detection

Some BDs can have several clips that have no audio (The Girl With the Dragon
Tattoo 2009).  This fools our audio selection logic into thinking the entire
BD has no audio.  So ignore clips that have no audio tracks when searching
for audio.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5127 b64f7644-9d1e-0410-96f1-a4d463321fa5