Merge branch 'jonbob/ocn/fix-0-ncells' (PR #6321)

Add logic to catch issue when partition file assigns 0 cells to a pe

When mpas-ocean runs with no cells assigned to a processor by a graph
file and has landIcePressureOn, the run aborts. This fixes that
situation by adding a check for the number of cells to the logic that
causes the abort.

Fixes: #6320

[BFB]

components/mpas-ocean/src/shared/mpas_ocn_diagnostics.F

@@ -181,7 +181,7 @@ subroutine ocn_diagnostic_solve(dt, statePool, forcingPool, meshPool, verticalMe
          call mpas_pool_get_array(forcingPool, 'landIceDraft', landIceDraft)
          call mpas_pool_get_array(forcingPool, 'landIceFloatingMask', landIceFloatingMask)
          call mpas_pool_get_array(forcingPool, 'landIceFraction', landIceFraction)
-         if (landIceFloatingMask(1) == -1) then
+         if (nCellsAll.gt.0 .AND. landIceFloatingMask(1) == -1) then
             call mpas_log_write('landIceFloatingMask contains the default value which likely indicates that this field is missing in the initial condition file (e.g. because it is meant for an older E3SM version).', &
                                 MPAS_LOG_CRIT)
          endif