[FIX] snailmail: Fix an error with invoice address

If an user tries sending a invoice using an invoice address and a
delivery address through snailmail, it would result in a traceback.
This is due to the invoice address record not having a name.

closes odoo/odoo#114171

X-original-commit: eceb23b1
Signed-off-by: Florian Daloze (fda) <fda@odoo.com>
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>