[FIX] stock: fix multi-step immediate transfer receipts

Steps to reproduce:
1. activate routes setting + multi-step incoming shipments (2 or 3,
   doesn't matter)
2. create an immediate transfer receipt
3. add a done quantity (optional: validate)
4. open corresponding 2nd step internal transfer

Expected result:
- amount done in immediate transfer receipt will be demand of internal
  transfer

Actual result:
- demand (and all other values) will be 0

closes odoo/odoo#68885

Task: 2492994
Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>