[V8][Sale - Product variants] Packaging not selectable in SO-line when variant not yet created

[roedeorm]

In a sale order line, the packaging can not be selected if the product variant has not been created yet.

This is how to replicate it: Create a product template with an attribute and two attribute values. Turn off automatic creation of product variants. Add a packaging to the product template. Manually create a product variant for one of the attribute values but do not create the product variant for the other attribute value. Open an SO and add an SO-line. Add the product template and select the attribute value for which the product variant has not been created yet. Try selecting the packaging. It will not work. The field stays empty. Now change to the attribute value for which the product variant has already been created. Try selecting the packaging. It works.

tested on 3154550-8-0-6bbddd on runbot1.odoo-community.org on 17.09.2016 around 02:00 CET