med_methods_FB_init creates fields with mismatched ungridded dimensions

Hi there,

I'm currently using CMEPs to couple CICE6, MOM6, and the UM and I noticed some unexpected behaviour while using CMEPS.

When ungridded dimensions are present, behaviour of `med_methods_FB_init` seems to depend on the internal field ordering of the input state. `med_methods_FB_init` removes `cpl_scalars` from the field name list `lfieldNameList`, but then accesses the fields from the input state by index when determining the ungridded dimensions. Unless `cpl_scalars` is the last field in the input state, this causes the wrong fields to be used when determining the ungridded dimensions of the output fields.

The following small change fixed this for my use case. Changing

https://github.com/ESCOMP/CMEPS/blob/d2a08f0edc84b30b91891d96d3dd0040a595db5e/mediator/med_methods_mod.F90#L451-L457

to

```
elseif (present(STflds)) then
call ESMF_StateGet(STflds, itemName=trim(lfieldnamelist(n)), field=lfield, rc=rc)
if (chkerr(rc,__LINE__,u_FILE_u)) return
```

Happy to submit a PR from my fork https://github.com/kieranricardo/CMEPS/tree/bugfix-FB-init-dim-mismatch if appropriate :)