Revert part of r187970, the NULL check was removed from udbp_bulk_read_complete() as well as udbp_attach.
Revert part of r187970, the NULL check was removed from
udbp_bulk_read_complete() as well as udbp_attach.

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