[FIX] stock: automatic orderpoint creation

When checking the replenishments, it sometimes creates a new reordering
rule for a product while another already exists.

To reproduce the error:
(Need purchase,sale_management)
1. Create a product P
	- Must be storable
	- In Purchase tab, add a vendor
2. Create a reordering rule for P
	- Trigger: Manual
	- Min: 0
	- Max: 0
3. Create+Confirm a SO with P
4. Go to Inventory > Operations > Replenishment
5. On P-product's line, click on "Order Once"
6. Confirm the generated RfQ
7. Repeat 3-4

Error: There are now two lines for P-product. A second reordering rule
has been automatically created but the first one does already the job.

OPW-2431780

closes odoo/odoo#65040

Signed-off-by: Adrien Widart <adwid@users.noreply.github.com>