BUG: fix setting zero magmoms

[lbluque]

Summary

With the new changes that set the default Sepcies.spin to None, I fixed the logic for setting zero magmoms in SpacegroupAnalyzer to check for None values as well.

Checklist

• Google format doc strings added. Check with ruff.
• Type annotations included. Check with mypy.
• Tests added for new features/fixes.
• If applicable, new classes/functions/modules have duecredit @due.dcite decorators to reference relevant papers by DOI (example)

Tip: Install pre-commit hooks to auto-check types and linting before every commit:

pip install -U pre-commit
pre-commit install

[shyuep]

Do you mind adding a unittest for one mag structure to check for this? I am worried that someone might make changes in future that breaks this again.

[shyuep]

Thanks!