In fact, that is correct. Even more, the message must be shown when there's no
incoming shipment only and in the assign_try button.
(grafted from d7fb4754552332ed9784fac21df98b2d977d2e45)
Make basic workflow work. Missing parts:
- Synchronize quantities between production and internal shipment
- Improve internal shipment or change shipment type so multiple locations can
be used in the same document.
- Allow using produced quantities as supplier invoice quantity