[FIX] stock: use docids as product_id in report

Steps to reproduce:

  - Install Inventory and Studio modules
  - Go to Inventory -> Products -> Products
  - Open Studio
  - Click on Reports tab
  - Select `Product Routes Report`

Issue:

  Traceback is raised.

Cause:

  No 'product_id' provided in data while getting report values.

Solution:

  If no `product_id` key or value in data, set `docids` (or an empty
  list if no docids) as product_id and set 'warehouse_ids'
  to an empty list.

opw-2619142

closes odoo/odoo#74860

Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>