libhb: fix BD audio detection problem
BDs can (and occasionally do) have different audio stream types in
different clips that compose a playlist.  We try to pick the audios that
appear in the most clips, but this breaks down when there are only 2
clips to choose from.  So in the case of only 2 clips, choose audio
from the longest clip.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5863 b64f7644-9d1e-0410-96f1-a4d463321fa5