[FIX] payment: False in reference
[FIX] payment: False in reference

- Activate a payment provider (e.g. Stripe)
- As an unconnected user, visit
  website_payment/pay?reference=MY_REF&amount=1337&acquirer_id=ACQUIRER
- Pay

After payment, the user is redirected to the `website_payment/confirm`
page. However, the generated reference contains `False`, which is
confusing.

This happens because the route is generated with the `False` string,
which is used later on in the computation reference.

We fix the URL generation by not adding the partner if it is not set.

opw-2201289

closes odoo/odoo#46277

X-original-commit: 7c5f5958a4ef20ac67ad6c87c3ea0c94b858a74b
Signed-off-by: Nicolas Martinelli (nim) <771435c469f83f6aa9c405ac5e1ed06314a94f2d@odoo.com>

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