[FIX] sale: pricelist recursion in without_discount

Supplements https://github.com/odoo/odoo/commit/0d56dca

When basing a pricelist on another pricelist in different currency
conversion was not being made correctly, since commit https://github.com/odoo/odoo/commit/6b3a808
that changes the pricelist_item on which the currency_id is set in
_get_real_price_currency.

Also align the _get_display_price's base_price to the
_onchange_discount's new_list_price in the case where the pricelist
depends on other pricelists that are in without_discount mode as well.