[FIX] website_sale: log if no pricelist

The pricelist field is not a mandatory field on the partner. A default
value is usually defined for any new partner created. However, if the
pricelist is manually removed from the partner, errors (tracebacks) will
occur in the eCommerce when no pricelist is found.

We cannot make the field mandatory, as it could potentially break the
workflow of some users which are not using eCommerce. Therefore, we
simply log an error message to help debugging.

opw-673453