Rework --correct-offset-shift to account for erroneous drive shifts due to intentional errors

[superg]

Some Datel discs make drive duplicate couple sectors right after intentional C2 errors area. Drive randomly corrects it later. As a consequence, generated image is invalid and never matches between dump attempts. --correct-offset-shift logic doesn't correct this because the shift is multiple of 588 samples (1 sector) and redumper cannot distinguish this case comparing to data lead-in/MSF shift. Make offset shift detection code aware of sessions and lead-in and treat everything else as offset shift.