surface_levelset: Fix a nasty bug
surface_levelset: Fix a nasty bug

Someone snuck a "0*" into the code in the subtlest way possible in
order to (1) slow down the code and (2) patch around an actual bug
in the bittlest way possible.  I'm not sure who.

omco/geode,omco/geode,omco/geode,omco/geode