improve error message when use_previous_directory workflows are improperly called

[jacksund]

Discussed in #528

^{Originally posted by SWeav02 November 2, 2023}
I've been working with a student from Northwestern Polytechnical University in China to help them use the code for BadELF. He's run into an error that seems to be thrown during the base workflow classes _load_input_and_register method before any of the body of the code is run.

For some background on the BadELF workflow that's being used, it's made to run on DFT calculations that have already been completed. When running on DFT calculations that weren't completed using Simmate, and therefore not stored in the database, I found that you need to prepare the settings.yaml file slightly differently from normal. You place the settings file outside of the directory with the VASP output files. Then set that directories name as the directory tag and the relative path to the POSCAR as the structure tag. I'm planning to eventually make it so that users can use BadELF through the command line instead, similar to the Henkelman Bader code, but for now this is what's worked for me.

The student sent me the output log and settings file that they used, which I'm attaching here. I haven't run into this error before and I'm not sure how to fix it. I'm hoping there's a simple solution.

output.log
settings.txt