Fine-tune of #59524.
If the delivery address doesn't have any delivery method assigned, you get an
undesired change of behavior: no delivery method is populated in that cases.
Note that the delivery method is not a commercial field that is propagated from
parent to children.
With this patch, we get a very similar behavior, which is fallbacking to the
commercial partner's delivery method if there's no delivery method in the delivery
address.
The only different behavior will be if the order partner is different from the
commercial partner of the delivery address.
closesodoo/odoo#60881
X-original-commit: 682b2e6c214b73f67e849df927bd4bda0af31d5a
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>