`dribble_crophrv_xsmrpool_2atm=.true.` crashes SASU runs

### Brief summary of bug

setting `dribble_crophrv_xsmrpool_2atm=.true.` crashes SASU runs, but AD and pSASU modes seem ok with this default setting

### General bug information

**CTSM version you are using:** [output of `git describe`]
`branch_tags/wetlands.n05.ctsm5.4.054`

**Does this bug cause significantly incorrect results in the model's science?** [Yes / No]
Unknown, but crashes SASU runs

**Configurations affected:** [Fill this in if known.]
SASU spinup only.
**As far as I can tell this is a new namelist setting, but I'm not sure where it came from?**

### Details of bug
AD and pSASU runs complete fine, but SASU run crashes with a C balance warning after ~18 months. As far as I can tell this is on a crop landunit in the tropics.

Case directory is:
`/glade/work/wwieder/clm6_cases/wetlands_CplHist_377_ne30_BgcCrop_178_SASU`

The case has failed twice now it the same spot with this error in the cesm.log

```
dec0496.hsn.de.hpc.ucar.edu 1995: cbalance warning at c = 18 7.114417033740536E-004
dec0496.hsn.de.hpc.ucar.edu 1995: 5702.21044018915
dec0496.hsn.de.hpc.ucar.edu 1995: column cbalance error = 7.114417033740536E-004 18
dec0496.hsn.de.hpc.ucar.edu 1995: is fates column? = F
dec0496.hsn.de.hpc.ucar.edu 1995: Latdeg,Londeg= -7.37580627510179 280.500000000000
dec0496.hsn.de.hpc.ucar.edu 1995: begcb = 5702.21718595468
dec0496.hsn.de.hpc.ucar.edu 1995: endcb = 5702.21044018915
dec0496.hsn.de.hpc.ucar.edu 1995: delta store = -6.745765530467907E-003
dec0496.hsn.de.hpc.ucar.edu 1995: --- Inputs ---
dec0496.hsn.de.hpc.ucar.edu 1995: gpp = 0.000000000000000E+000
dec0496.hsn.de.hpc.ucar.edu 1995: --- Outputs ---
dec0496.hsn.de.hpc.ucar.edu 1995: er = 1.559041457422894E-002
dec0496.hsn.de.hpc.ucar.edu 1995: col_fire_closs = 0.000000000000000E+000
dec0496.hsn.de.hpc.ucar.edu 1995: col_hrv_xsmrpool_to_atm = 0.000000000000000E+000
dec0496.hsn.de.hpc.ucar.edu 1995: col_xsmrpool_to_atm = -9.556090747057870E-003
dec0496.hsn.de.hpc.ucar.edu 1995: wood_harvestc = 0.000000000000000E+000
dec0496.hsn.de.hpc.ucar.edu 1995: crop_harvestc_to_cropprodc = 0.000000000000000E+000
dec0496.hsn.de.hpc.ucar.edu 1995: -1*som_c_leached = 7.722170963320667E-014
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: local column index = 18
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: global column index = 34362
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: global landunit index = 16070
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: global gridcell index = 8012
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: landunit type = 2
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: column type = 267
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: gridcell longitude = 280.5000000
dec0496.hsn.de.hpc.ucar.edu 1995: iam = 1867: gridcell latitude = -7.3758063
dec0496.hsn.de.hpc.ucar.edu 1995: WARNING: Trouble getting the 2D gridcell indices
dec0496.hsn.de.hpc.ucar.edu 1995: ENDRUN:
dec0496.hsn.de.hpc.ucar.edu 1995: ERROR in CNBalanceCheckMod.F90 at line 384
```
Setting `dribble_crophrv_xsmrpool_2atm=.false.` fixes this issue in SASU runs

see also discussion on [LMWG_dev_#178](https://github.com/NCAR/LMWG_dev/issues/178)