[FIX] mail: Keep backward compatibility on route /mail/view
[FIX] mail: Keep backward compatibility on route /mail/view

- If a database is migrated from an older version to saas-11.3 without
this patch, all the links /mail/view with a message_id as parameter will not work.
  We must keep the backward compatibility for those links.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo