Stevens Pass Route loading bug fixed in v74.8a on 64-bit

Add the "StevensPassAssetsRailNetwork.ap" file to the "RailWorks\Assets\GNTX\StevensPass" path.

Observation: If for some reason you extracted StevensPassAssets.ap, you are also required to extract the StevensPassAssetsRailNetwork.ap patch and replace the existing files, otherwise it will never work, as the simulator has a files reading rules.