**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


return self.env['product.product']._convert_prepared_anglosaxon_line(line, part)
    @api.multi
    def action_cancel(self):
        moves = self.env['account.move']
        for inv in self:
            if inv.move_id:
                moves += inv.move_id
            if inv.payment_move_line_ids:
                raise UserError(_('You cannot cancel an invoice which is partially paid. You need to unreconcile related payment entries first.'))
        
        self.write({'state': 'cancel', 'move_id': False})
        if moves:
            
            moves.button_cancel()
            
            
            
            moves.unlink()
        return True
    
    @api.multi
    def name_get(self):