MAPL develop breaks upper-air remapping

[mathomp4]

This appears to be a similar issue as #3307 (which was closed in #3310 ). In my nightly tests, the remap_upper step (aka interp_restarts.x) fails with:

...
   70   13.134803    0.9419    954.9999    14.9997
   71    6.593752    0.9634    969.9998    14.9999
   72    0.048048    0.9850    985.0000    15.0002
   73    0.000000    1.0000   1000.0000    15.0000

  Total Number of Tracers in  MOIST:    648   (/KM =    9.00)

Abort(134824965) on node 11 (rank 11 in comm 0): Fatal error in PMPI_Comm_dup: Unknown error class, error stack:
PMPI_Comm_dup(166): MPI_Comm_dup(MPI_COMM_NULL, new_comm=0x7fffaa9ba038) failed
PMPI_Comm_dup(123): Null communicator
Abort(403260421) on node 12 (rank 12 in comm 0): Fatal error in PMPI_Comm_dup: Unknown error class, error stack:
PMPI_Comm_dup(166): MPI_Comm_dup(MPI_COMM_NULL, new_comm=0x7ffff2122fb8) failed
PMPI_Comm_dup(123): Null communicator
...

There are no obvious communicator uses in there (or in fv_regrid_c2c.F90) to me, but I hope @atrayano can see something.

I'll also assign @bena-nasa only because he probably knows this code better than any of us.