Proper handling of empty attribute when minLength=1

          Ok, for our desired use case, this causes eido validation to fail:

    _validate_sample_object(
  File "/home/drc/GITHUB/looper/master/looper/venv/lib/python3.10/site-packages/eido/validation.py", line 100, in _validate_sample_object
    _validate_object(sample.to_dict(), sample_schema_dict)
  File "/home/drc/GITHUB/looper/master/looper/venv/lib/python3.10/site-packages/eido/validation.py", line 47, in _validate_object
    instance_name = error.instance[sample_name_colname]
IndexError: string index out of range

This is because error.instance is empty and sample_name_colname=False

However, if you do have some value in the field such as 'h' but the minLength: 2, we see a better message:

Error: EidoValidationError (Validation failed): {"'h' is not valid under any of the given schemas": [{'type': "'h' is not valid under any of the given schemas", 'message': "'h' is not valid under any of the given schemas on instance h", 'sample_name': 'h'}]}
["'h' is not valid under any of the given schemas"]

Originally posted by @donaldcampbelljr in https://github.com/pepkit/looper/issues/523#issuecomment-2560016083

Start in eido/validation.py, especially _validate_sample_object and _validate_object, and reproduce the empty-value case with minLength=1. Compare it with the non-empty minLength failure shown in the issue; done means empty attributes no longer trigger an IndexError and validation reports the failure consistently.