Noticed by @minohaka, following rP22313 units no longer collected nearby resources after depleting one.
The cause for this is that the old code, in Order.Gather, started moving right away and put us in APPROACHING state. This failed, but that failure didn't actually change our state. Then MoveCompleted() was triggered (probably errored out), and this put us in GATHERING state, which did correctly handle returning to collect resources.
I think this "find nearby resources" code should be moved to another state, but in the meantime this fixes the issue appropriately, and adds a test case for it.