[FIX] website_form: custom file -> mail attachments
[FIX] website_form: custom file -> mail attachments

There was a code that on:

- a form that sent a mail
- with a custom file field

would set the file as attachments, but the code was dead because of a
typo in `if` statement order.

opw-1906883
closes #28525
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo