fix(validation): prevent siret to be False

[lermit]

Hello

In the get_directory_lines_parsed function we can have a bug if the customer company is a private one.

In this case the siret variable is False.

Workflow :

1/ Odoo call the get_directory_lines_parsed function with the partner siren in siren_or_siret variables
2/ line 597 the siret variable is set to False
3/ line 625 the dir_siret is set to siret returned by directory
4/ line 746 expected_identifier is construct with siren_siret where siret is False
5/ line 750 expected_identifier is compared to identifier returned by Directory (SuperPDP in my test). Test fail

I'm not sure my solution is the correct one but this one allow e-invoicing private company.

Thank you very very very much for your work on the e-invoicing intégration for Odoo. Your work is awesome !

Regards