Bug: Post box pretends it has cargo attribute

[[C] Ranran]

Hi.


I believe the postbox box has no cargo attribute, but the icon has a brown mass. (´・ω・｀)騙したのね？
https://github.com/jamespetts/simutrans-pak128.britain/blob/master/stations/bus-stops.dat

James's repository:
https://raw.githubusercontent.com/jamespetts/simutrans-pak128.britain/master/stations/loading-bay.png

In the neroden's repository it has been fixed.
https://raw.githubusercontent.com/neroden/simutrans-pak128.britain/ncn-devel/stations/loading-bay.png

[[C] Ranran]

I corrected the icon and threw a pull request.
https://github.com/jamespetts/simutrans-pak128.britain/pull/60/commits

I mistakenly wrote "bus stop" in commit, but please miss it.

[jamespetts]

Thank you for this report and fix - now incorporated.