Merge pull request #40 from billsacks/usrf0_consistency

Make usrf condition in is_in_active_grid consistent with other checks

As per suggestions from Bill Lipscomb in
#39, I am treating usrf == 0 as
land rather than ocean. This makes the conditional here consistent with
similar checks elsewhere in CISM.

libglad/glad_output_states.F90

@@ -119,11 +119,13 @@ logical function is_in_active_grid(geometry, i, j)
 
     ! TODO(wjs, 2015-03-18) Could the logic here be replaced by the use of some existing
     ! mask? For now I am simply re-implementing the logic that was in glint.
+    !
+    ! (2021-08-31) See also comments in https://github.com/ESCOMP/CISM/issues/39
 
     usrf = thk0 * geometry%usrf(i,j)
 
-    if (usrf > 0.d0) then
-       ! points not at sea level are assumed to be land or ice sheet
+    if (usrf >= 0.d0) then
+       ! points at or above sea level are assumed to be land or ice sheet
        is_in_active_grid = .true.
     else
        is_in_active_grid = .false.