Fix bug in boundary_k_range if hbl > htot

In cases where the boundary layer depth is larger than the column thickness,
the returned indices of the layer would point to the top of the column. This
behavior is fixed such that if hbl > htot, k_bot and z_bot point to the bottom
of the column.

src/tracer/MOM_lateral_boundary_diffusion.F90

@@ -338,6 +338,11 @@ subroutine boundary_k_range(boundary, nk, h, hbl, k_top, zeta_top, k_bot, zeta_b
     k_bot = 1
     zeta_bot = 0.
     if (hbl == 0.) return
+    if ( hbl >= htot ); then
+      k_bot = nk
+      zeta_bot = 0.
+      return
+    endif
     do k=1,nk
       htot = htot + h(k)
       if ( htot >= hbl) then
@@ -354,10 +359,15 @@ subroutine boundary_k_range(boundary, nk, h, hbl, k_top, zeta_top, k_bot, zeta_b
     zeta_bot = 1.
     htot = 0.
     if (hbl == 0.) return
+    if (hbl >= htot) then
+      k_top = 1
+      zeta_top = 0.
+      return
+    endif
     do k=nk,1,-1
       htot = htot + h(k)
       if (htot >= hbl) then
-        k_top = k
+      k_top = k
         zeta_top = 1 - (htot - hbl)/h(k)
         return
       endif