Fix panic introduced by me in r240835, when zero weight was passed to wtab_alloc().
Fix panic introduced by me in r240835, when zero weight
was passed to wtab_alloc().

Reported by:	Kim Culhan <w8hdkim gmail.com>

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