DVB teletext streams and ATSC AC3 audio streams use the same code points. If we miscl...

DVB teletext streams and ATSC AC3 audio streams use the same code points. If we misclassify teletext as audio we'll die early in the encode while trying to find an AC3 sync frame. So, if we don't find a sync frame after searching a megabyte of the stream decide it's not AC3, delete the audio entry & keep going.
Problem & test case from ncbp http://forum.handbrake.fr/viewtopic.php?p=29137#p29137.

git-svn-id: svn://localhost/HandBrake/trunk@1325 b64f7644-9d1e-0410-96f1-a4d463321fa5