When a PO is in the "To Approve" state, it disappears from the
forecasted report

To reproduce the issue:
1. In Settings, enable "Purchase Order Approval" with a minimum amount
equal to 0
2. Create a storable product P
3. With Marc Demo:
    - Create a PO with 50 x P
    - Consult the forecasted report of P: there are 50 x P "Forecasted +
Pending"
    - Confirm the PO (its state becomes "To Approve")
    - Consult the forecasted report of P

Error: The 50 x P disappeared: 0 On Hand, 0 Forecasted, 0 Forecasted +
Pending. We should still see 50 Forecasted + Pending

OPW-2774586

closes odoo/odoo#86161

Signed-off-by: Arnold Moyaux <arm@odoo.com>