PMO should only look at the write_output_state_to_file item, not the filename(s)

if you have this in your PMO namelist:

   write_output_state_to_file = .false.
   output_state_files         = ""

then helen's recent fix prevents a coredump and it exits with a message saying you have to specify an output filename.

but if you have this:

   write_output_state_to_file = .false.
   output_state_files         = "bob.nc"

then pmo runs fine, and doesn't create an output file. the logic here is broken.

Describe the bug

1. download a caminput.nc from the /glade/p/cisl/dares/DART_test_cases into your models/cam-fv/work dir
2. build the cam-fv executables
3. in input.nml, change write_output_state_to_file to .false.
4. run - it finishes fine and doesn't create perfect_restart.nc
5. in input.nm, change output_state_files to "" (2 double quotes)
6. run - it gives you an error that you have to specify an output file (or it coredumps if you don't have helen's latest update downloaded)

it should ignore the filename if you're not writing output.

Start with the PMO logic that reads write_output_state_to_file and output_state_files from input.nml, using the cam-fv/work reproduction steps as the first check. Done means a false write_output_state_to_file setting no longer requires an output filename and produces no output file, including when output_state_files is empty.