Steps to reproduce the bug:
- Create two storable products:
    - kit_1 and Comp_1
- Create a bill of materials:
    - Product: kit_1
    - Type: Kit
    - Components: 1 unit of Comp_1
- Create a SO with:
    - kit: 1 unit
    - Confirm the SO
- A picking with 2 units of “comp_1” will be created

- Edit SO:
    - Reduce the qty of kit_1 to 0

Problem:
“Comp_1” qty not updated to 0 on the picking.

When the SOL qty is updated, the pickings should be updated too.
So we get the qty in delivery:
https://github.com/odoo/odoo/blob/e11dfa341baf82fedee753502aef5ef2972f75cb/addons/sale_stock/models/sale_order.py#L553

then the difference between that qty and the new SOL qty is computed.
And procurement based on that difference is created:
https://github.com/odoo/odoo/blob/e11dfa341baf82fedee753502aef5ef2972f75cb/addons/sale_stock/models/sale_order.py#L573-L578

but the `_get_qty_procurement` function returns 0 as result, because
the `_compute_kit_quantities` function is called with the qty set on
the SO (“0”), so the result will be 0 because we need 0 qty to have 0
kit:
https://github.com/odoo/odoo/blob/4ee5df76607c80c94a4aea832dcd2f73ad8e5ee1/addons/sale_mrp/models/sale_order_line.py#L121-L122



opw-3018258

closes odoo/odoo#104631

Signed-off-by: William Henrotin (whe) <whe@odoo.com>