Infinite mail capacity in some airplanes

[DaleStan]

In the PlaneSet, the Zeppelins reproducibly have an infinite mail capacity.

To reproduce, send a Zeppelin on a useful trip, and set to full load. Especially if fullloadany is on, or mail is produced one bag at a time, it may take a while for this bug to manifest, so here's a save (vehicle multiplier 4). Just in case it matters, I included the copy of the PlaneSet I'm using.
Watch Airplane 1, which is just about to land at Henningstone Central.

Since I could not reproduce this bug with the Chinook (which replaces a chopper, while the Zeps replace planes), I'm guessing that this bug has something to do with attaching a rotor to a vehicle that didn't originally have one.

I am using TTDPatch 2.0.1 alpha 42.