Fix fencepost error causing creation of 0-length mbufs when the boundary  between header and data fell on the boundary between two mbufs.
Fix fencepost error causing creation of 0-length mbufs when the boundary
 between header and data fell on the boundary between two mbufs.

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