[FIX] sale_management: uom not displayed to the customer

The uom must be displayed to the customer in any case.
Otherwise a customer couldn't know the modalities of a contract
(ex: a contract of one year or one day)

Fine tuning of 342dd5ff

opw:2411108

closes odoo/odoo#65037

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>