Divide-by-zero in advance_windm_edsclrm_module.F90

Ran into this error with ne120-wcycl runs (`SMS_D.ne120_oRRS18v3_ICG.A_WCYCL1950S_CMIP6_HR.theta_intel.cam-cosplite`)
```
3439: forrtl: error (73): floating divide by zero
3439: Image PC Routine Line Source
3439: e3sm.exe 000000000375F18D advance_windm_eds 1891 advance_windm_edsclrm_module.F90
3439: e3sm.exe 000000000374C6CA advance_windm_eds 509 advance_windm_edsclrm_module.F90
3439: e3sm.exe 000000000370A989 advance_clubb_cor 2019 advance_clubb_core_module.F90
3439: e3sm.exe 00000000021A0930 clubb_intr_mp_clu 1855 clubb_intr.F90
3439: e3sm.exe 0000000000D31B4B physpkg_mp_tphysb 2460 physpkg.F90
3439: e3sm.exe 0000000000D0848F physpkg_mp_phys_r 1027 physpkg.F90
3439: e3sm.exe 000000000081FFA5 cam_comp_mp_cam_r 250 cam_comp.F90
3439: e3sm.exe 00000000007EF416 atm_comp_mct_mp_a 341 atm_comp_mct.F90
3439: e3sm.exe 00000000004557E3 component_mod_mp_ 267 component_mod.F90
3439: e3sm.exe 000000000042A297 cime_comp_mod_mp_ 1958 cime_comp_mod.F90
3439: e3sm.exe 000000000044B66B MAIN__ 92 cime_driver.F90
```

This can be prevented by the following patch:
```
diff --git a/components/cam/src/physics/clubb/grid_class.F90 b/components/cam/src/physics/clubb/grid_class.F90
index 1a68eec59..e28aa45fe 100644
--- a/components/cam/src/physics/clubb/grid_class.F90
+++ b/components/cam/src/physics/clubb/grid_class.F90
@@ -718,6 +718,10 @@ module grid_class
! Define invrs_dzm, which is the inverse spacing between thermodynamic grid
! levels; centered over momentum grid levels.
do k=1,gr%nz-1
+ if (gr%zt(k+1) - gr%zt(k) == 0) then
+ write(fstderr,*) 'Detected div-by-0 with gr%zt', k,gr%nz,gr%zt(k+1),gr%zt(k)
+ stop
+ endif
gr%invrs_dzm(k) = 1._core_rknd / ( gr%zt(k+1) - gr%zt(k) )
enddo
gr%invrs_dzm(gr%nz) = gr%invrs_dzm(gr%nz-1)
@@ -726,6 +730,10 @@ module grid_class
! Define invrs_dzt, which is the inverse spacing between momentum grid
! levels; centered over thermodynamic grid levels.
do k=2,gr%nz
+ if (gr%zm(k) - gr%zm(k-1) == 0) then
+ write(fstderr,*) 'Detected div-by-0 with gr%zm', k,gr%nz,gr%zm(k),gr%zm(k-1)
+ stop
+ endif
gr%invrs_dzt(k) = 1._core_rknd / ( gr%zm(k) - gr%zm(k-1) )
enddo
gr%invrs_dzt(1) = gr%invrs_dzt(2)
```

This is only for better error-checking and might save some time chasing it the next time it happens.