[FIX] product: display pricelists that have no defined end date

Steps to reproduce the bug:
- Go to purchase > Configuration > Vendor Pricelists
- Filters > select the “Active” filter

Problem:
Currently, the filter does not include records that do not have a specified `”date_end”`, even though they are considered active.

Opw-2659829

closes odoo/odoo#78623

X-original-commit: bb8bef5c
Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>
Signed-off-by: Djamel Touati <DjamelTouati@users.noreply.github.com>