We can't expect a multiple of 8 during marker search.

Once the marker was on a position not matching a multiple of
8 from the end, the search would fail. Now decrement by 1 byte.

Change-Id: Ia703c9074b3bef6b1a300865abfe24dcb2c8d5fd
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Niels Weber <niels.weber@digia.com>