Finished EmitCargoOnSell

The broken Lint check is still a problem after all those years. This also does not work as suggested in the empty trait. During selling it destroys the cargo so you can't just queue an Unload activity. You can't even enumerate through all passengers without hitting crashes. However, unloading just the first passenger is good enough for Red Alert's single-manned pillboxes.
I tried

```csharp
		public void Sold(Actor self)
		{
			if (Info.EjectOnSell && cargo != null)
				foreach (var c in cargo)
					Unload(self);
		}
```

but that does not help at all with `System.InvalidOperationException: Collection was modified; enumeration operation may not execute.`