Issue description
I have a cargo depot that has been unassigned from a contract. An attached fluid module is emptied by trucks except for the last 25 sour water. 'Allow partially loaded trucks' is set,, but the trucks won't remove the remaining items. There is a fluid storage requesting the sour water and idle trucks. The same behaviour happens with a fluid storage, but they have a control to 'remove currently assigned products' (dustbin icon) The same control on a cargo depot fluid module is dimmed. If I delete the fluid module, the sour water disappears, i.e. it doesn't get transferred to another storage.
The same problem happens on the cargo depot itself trying to unload fuel for the ship. That doesn't have a control to remove currently assigned fuel and similarly if I delete the cargo depot the fuel disappears.
Reproduction steps
Try to unload all product from cargo depot fluid module.
Game version and build number
v0.6.4d b343
Operating system
Windows
