[BUG]: GITM can't compile with Nag fortran compiler

[abukowski21]

A couple of things prevent GITM from compiling with Nag compiler. Some use nag - and SWMF is tested with Nag - so it is worthwhile to fix this.

The problems I'm aware of:

• A couple of character length issues. For example, src/ModHmeModel.f90 should use * instead of iCharLenHme_
• src/ModSami.f90 '(L)' -> * in line read(iSamiUnit, '(L)', iostat=iError) CorotationAdded
• Nan checks. For example if (any(ieee_is_nan(geopt))) then instead of if (count(isnan(geopt)) >0) then

These are the errors I know of now, but there could be more

[abukowski21]

Talked with Gabor just now. The issue is with intent(in) strings. When the string is passed from another routine, it can (should?) use len=*. Then other strings can use the LEN() of that, if necessary. Then allegedly Fortran has support to automatically allocate string lengths. So we may not even need to set a length. Not sure which versions of fortran compilers that's true for.

So I'll tackle this one

Of course, related to #14 .