[FIX] delivery: default company in price computation

- Set the company currency in USD
- Create a pricelist in EUR
- Create a SO with the EUR pricelist
- Add a stockable product
- Click on 'Add Shipping'
- Select 'Normal Delivery Charges' which has a fixed price

The price is not updated according to the USD - EUR exchange rate.

This happens because no company is set on the delivery method, so no
conversion is performed.

We fall back on the order company, then the current environement
company.

opw-2159838

closes odoo/odoo#43119

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/delivery/models/delivery_carrier.py

@@ -257,8 +257,9 @@ class DeliveryCarrier(models.Model):
                     'error_message': _('Error: this delivery method is not available for this address.'),
                     'warning_message': False}
         price = self.fixed_price
-        if self.company_id and self.company_id.currency_id.id != order.currency_id.id:
-            price = self.company_id.currency_id._convert(price, order.currency_id, self.company_id, fields.Date.today())
+        company = self.company_id or order.company_id or self.env.company
+        if company.currency_id and company.currency_id != order.currency_id:
+            price = company.currency_id._convert(price, order.currency_id, company, fields.Date.today())
         return {'success': True,
                 'price': price,
                 'error_message': False,