fix a problem with point-to-point hanging when searching for start point

fix a problem with point-to-point hanging when searching for start point
in reader, the timestamps were not being correctly adjusted for scr offset
before comparing to start time.  This could cause an early start in reader.
Then in sync, syncAudioWork stalled until the correct start of video was
found, causing the audio fifo to fill and stall the whole pipeline.

git-svn-id: svn://localhost/HandBrake/trunk@3329 b64f7644-9d1e-0410-96f1-a4d463321fa5