[FIX] sale_purchase_stock: correct PO deadline date

steps to reproduce it:
1. Create a storable product, add a Purchase vendor with
 start date = 20/6/2022 and delay = 56
2. Create another storable product, add the same Purchase vendor with
 start date = 11/01/2023 and delay = 21
3. For both products, add Routes "MTO".
4. Create a SO with those 2 products, and confirm it
5. As you can see, the price of the first product is correctly set
but not the second product

BUG:
This is due of "Order Deadline" (date_order) being set to an old date,
which is before the second product date_order.

FIX:
set max PO date as today

opw-3167094

closes odoo/odoo#124448

Related: odoo/enterprise#44391
Signed-off-by: William Henrotin (whe) <whe@odoo.com>