Zero diffusivity at boundary edges

Explicitly sets diffusivity to zero at boundary edges, instead of just
waterFluxDiff

components/mpas-albany-landice/src/mode_forward/mpas_li_subglacial_hydro.F

@@ -1018,6 +1018,7 @@ subroutine calc_edge_quantities(block, err)
          endif
       end do
       where (waterFluxMask == 2)
+         diffusivity = 0.0_RKIND
          waterFluxAdvec = 0.0_RKIND
          waterFluxDiffu = 0.0_RKIND
          waterVelocity = 0.0_RKIND