Fix a '<<' that should have been a '>>' in the 48bit case.
Fix a '<<' that should have been a '>>' in the 48bit case.

Fortunately we only have had 32bit block counts until recently,
and no 2TB disks :)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase