NoAnthro test fails when checking for stream_meshfile_popdens file as it's none

[ekluzek]

Brief summary of bug

NoAnthro use test case fails in the build-namelist unit tester

406/1740 < FAIL> <Test Id: 406> <Desc: -res 0.9x1.25 -bgc bgc -use_case 1850_noanthro_control -drydep -fire_emis -light_res 360x720 -phys clm5_0: lnd_in file exists>

General bug information

CTSM version you are using: ctsm5.1.dev044
**Does this bug cause significantly incorrect results in the model's science?**No
Configurations affected: NoAnthro use case

Important details of your setup / configuration so we can reproduce the bug

It does list the file as none in 'Buildconf/ctsm.input_data_list, but check_input_data safely seems to ignore it.

Important output or errors that show the problem

The error it shows is:

CLM adding use_case 1850_noanthro_control defaults for var 'stream_meshfile_popdens' with val 'none'
ERROR : CLM build-namelist::CLMBuildNamelist::add_default() : file not found: stream_meshfile_popdens = /glade/p/cesmdata/cseg/inputdata/none