NDPI: fix tile offset adjustment for files larger than 4GB

Fixes http://trac.openmicroscopy.org/ome/ticket/12367.  To test, verify that each of the files in ```data_repo/from_skyking/hamamatsu/kristian``` can be imported into OMERO, and that the resulting images can be viewed and do not look obviously wrong.  The NDP.view software (http://www.hamamatsu.com/jp/en/U12388-01.html#1328463611394) can also be used to verify that the images are correct.

All builds are expected to remain green with this PR included.