Fixes #5149.

Fixes #5149.
Ensures that items delivered using the cargo delivery office conveyor belt is either properly sent on through the station or towards disposals.

Tested a few different designs but in the end this is the best I could come up with that allows both trash and tagged items to travel through properly:
https://www.dropbox.com/s/dszoyucn6mp493f/DisposalPreview.png?dl=1