top level folder is used before reading JSON settings

[jolopezl]

I have in backend.json a field for the top_level_folder:

~/temp/CARTAvis/carta-backend/build (dev)$ cat ~/.carta/backend.json | grep top_level_folder
    "top_level_folder": "/Users/lopez/temp/CARTAvis",

If I start carta, and do:

$ ./carta_backend ~/temp/CARTAvis/data/supermosaic.10.hdf5 

I get the following address:

http://localhost:3020/?token=2E47A4E8-A420-4507-A8DD-66ED2F6EA7A7&file=Users%2Flopez%2Ftemp%2FCARTAvis%2Fdata%2Fsupermosaic.10.hdf5

Which, as you can see is incorrect. It actually does not exist, and CARTA will not open it. I mentioned before that I needed to edit it by hand, because the URL should have resulted in something relative to my top_level_folder. Now, following KS example, I set the top_level_folder to on the command line, overriding my settings, then start CARTA as:

$ ./carta_backend --top_level_folder ~/temp/CARTAvis ~/temp/CARTAvis/data/supermosaic.10.hdf5

Which parses the correct URL:

http://localhost:3020/?token=6E6DD32E-3642-4235-A1D4-283BBA890B4B&file=data%2Fsupermosaic.10.hdf5

The problem is here: https://github.com/CARTAvis/carta-backend/blob/dev/src/Main/ProgramSettings.cc#L375-L382. The files are pushed before the JSON settings override the command line settings which come first, so top_level_folder is "" at that moment.