MPAS freezes if 'Time' dimension in input file is not unlimited

[matthewhoffman]

If the 'Time' dimension in the input file is not unlimited (e.g. just has a size of 1, but without the unlimited condition enabled), MPAS freezes during init. The log simply says:
"Reading namelist.input"
with no additional information, and the run seems to get 'stuck'. On hopper, the job eventually goes out of memory. On my laptop, it completely froze up my machine and I had to manually do a hard restart of my system.

@douglasjacobsen and I had looked into this briefly awhile ago, and if I remember correctly the issue was happening inside PIO. I don't remember anymore than that.

On my laptop I am using:
MPAS 2.0
pnetcdf 1.3.1
pio Revision: 835 (1_7_2)

On hopper we are using:
MPAS 2.0
pnetcdf 1.3.1
pio 1_7_1

I think it would be desirable if the time dimension is not required to be unlimited, but if that is not an option, I would be happy if there was some sort of error printed and a clean abort rather than the whole thing freezing.

This is not a high priority issue, but I am adding it before I forget about it.

[douglasjacobsen]

For reference, an "unlimited" dimensions file can be converted into a "limited" time dimension file using:
ncdump grid.nc | sed "s/UNLIMITED/1/g" | ncgen -o limited_grid.nc -

[douglasjacobsen]

I think this is fixed, but @matthewhoffman reopen if you see this again.