libhb: fix crashes with some BDs
A stray line of code from the switch from mpeg2dec to
libavcodec caused a failure to open the mpeg2 decoder for BDs


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6009 b64f7644-9d1e-0410-96f1-a4d463321fa5