[FIX] purchase_stock: Wrong journal entry created from vendor bill

Steps to reproduce:

- Create a storable product P with a vendor V and a purchase price = 100€
- Set the category of the prodcut to automated and AVCO and set a price diff account on it
- Create PO for V with 10 P with a price_unit = 110€
- Confirm the PO and deliver 7 P with no backorder
- Change the ordered quantity of P to 9 on PO (and the unit_price will be set to 100€)
- Go on the delivery order and deliver 2 remainig P
- Create the invoice and validate it

Bug:

The amount due on the invoice was 900.02€ instead of 900.00€

PS: The debit and credit of an aml are computed with the price (defined in function
_anglo_saxon_purchase_move_lines) with the function _convert_prepared_anglosaxon_line
defined on model account.invoice. So rounding the price unit after the computation
of the price allows to keep the same total as the one computed for the PO.

opw:1951465

closes odoo/odoo#32345

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>

addons/purchase_stock/models/account_invoice.py

@@ -123,7 +123,7 @@ class AccountInvoice(models.Model):
                             diff_line = {
                                 'type': 'src',
                                 'name': i_line.name[:64],
-                                'price_unit': inv.currency_id.round(price_unit_val_dif),
+                                'price_unit': price_unit_val_dif,
                                 'quantity': line_quantity,
                                 'price': inv.currency_id.round(price_val_dif),
                                 'account_id': acc,
@@ -133,8 +133,9 @@ class AccountInvoice(models.Model):
                                 'tax_ids': tax_ids,
                             }
                             # We update the original line accordingly
-                            line['price_unit'] = inv.currency_id.round(line['price_unit'] - diff_line['price_unit'])
+                            line['price_unit'] = line['price_unit'] - diff_line['price_unit']
                             line['price'] = inv.currency_id.round(line['quantity'] * line['price_unit'])
+                            line['price_unit'] = inv.currency_id.round(line['price_unit'])
                             diff_res.append(diff_line)
             return diff_res
         return []