[IMP] website_portal_sale: prevent partner changes if invoices exist
[IMP] website_portal_sale: prevent partner changes if invoices exist

We should not allow a partner to *easily* change its invoicing data
if invoices have already been issued to him.

dfang/odoo,dfang/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,ygol/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,dfang/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo