**Impacted versions:**
* 9.0

**Steps to reproduce:**
* Enable multi currencies
* Make sure that the current rate of a foreign currency (i.e. EUR) is not 1.0 (i.e. 0.84)
* Create a purchasable product with a cost (i.e. 33$)
* Create a vendor bill in a foreign currency (i.e. EUR)
* Add the product on the invoice

**Current behavior:**
* The unit price will be 23.28 == (33 * 0.84) * 0.84

**Expected behavior:**
* The unit price should be 27,72 == 33 * 0.84
* Probably due to this line of code: https://github.com/odoo/odoo/blob/9.0/addons/account/models/account_invoice.py#L1241

**Video/Screenshot link (optional):**
* On Runbot Community 9.0: https://www.youtube.com/watch?v=60qPmczo5vk


_inherit = "product.product"
    @api.model
    def _convert_prepared_anglosaxon_line(self, line, partner):
        return {
            'date_maturity': line.get('date_maturity', False),
            'partner_id': partner,
            'name': line['name'],
            'debit': line['price'] > 0 and line['price'],
            'credit': line['price'] < 0 and -line['price'],
            'account_id': line['account_id'],
            'analytic_line_ids': line.get('analytic_line_ids', []),
            'amount_currency': line['price'] > 0 and abs(line.get('amount_currency', False)) or -abs(line.get('amount_currency', False)),
            'currency_id': line.get('currency_id', False),
            'quantity': line.get('quantity', 1.00),
            'product_id': line.get('product_id', False),
            'product_uom_id': line.get('uom_id', False),
            'analytic_account_id': line.get('account_analytic_id', False),
            'invoice_id': line.get('invoice_id', False),
            'tax_ids': line.get('tax_ids', False),
            'tax_line_id': line.get('tax_line_id', False),
        }