[FIX] purchase: Scheduled Date in PO
[FIX] purchase: Scheduled Date in PO

When setting the quantity in a PO line, the field "date_planned" is changed
by onchange_product_id and this field is equal to:
-the date of today + seller.delay if there is at least one provider for the product
-the date of today if there is no provider set for the product
-the date manually set if there is no provider and already a scheduled_date set

To keep the similar behaviour to 8.0 for product without provider.

opw:652394

laslabs/odoo,Elico-Corp/odoo_OCB,hip-odoo/odoo,storm-computers/odoo,storm-computers/odoo,dfang/odoo,hip-odoo/odoo,stephen144/odoo,ygol/odoo,ygol/odoo,stephen144/odoo,syci/OCB,sysadminmatmoz/OCB,storm-computers/odoo,Elico-Corp/odoo_OCB,storm-computers/odoo,hip-odoo/odoo,ygol/odoo,syci/OCB,hip-odoo/odoo,optima-ict/odoo,sysadminmatmoz/OCB,dfang/odoo,stephen144/odoo,sysadminmatmoz/OCB,bplancher/odoo,optima-ict/odoo,bplancher/odoo,stephen144/odoo,microcom/odoo,Elico-Corp/odoo_OCB,microcom/odoo,hip-odoo/odoo,sysadminmatmoz/OCB,storm-computers/odoo,bplancher/odoo,dfang/odoo,laslabs/odoo,sysadminmatmoz/OCB,ygol/odoo,ygol/odoo,stephen144/odoo,Elico-Corp/odoo_OCB,syci/OCB,bplancher/odoo,sysadminmatmoz/OCB,bplancher/odoo,bplancher/odoo,hip-odoo/odoo,microcom/odoo,ygol/odoo,stephen144/odoo,ygol/odoo,syci/OCB,Elico-Corp/odoo_OCB,microcom/odoo,optima-ict/odoo,microcom/odoo,laslabs/odoo,syci/OCB,sysadminmatmoz/OCB,laslabs/odoo,optima-ict/odoo,laslabs/odoo,laslabs/odoo,dfang/odoo,storm-computers/odoo,optima-ict/odoo,microcom/odoo,optima-ict/odoo,dfang/odoo,Elico-Corp/odoo_OCB,syci/OCB,dfang/odoo