[FIX] product: prevent ValueError when computing quantity on a void recordset
[FIX] product: prevent ValueError when computing quantity on a void recordset

Invoice lines do not necessarily have a product and therefore an UoM set
on them. You could then compute quantityes on a void recordset. In that
case we just return the quantity untouched.

This is actually the old behavior of compute_quantity that is set back.
See https://github.com/odoo/odoo/blob/01279359b9e5340d5ecb15f0fee186f039356374/addons/product/product.py#L164 .

Closes #16377

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