Automatic merge of T1.5.1-919-gf19642ebc and 15 pull requests

- Pull request #570 at 3539862: Experimental glTF 2.0 support with PBR lighting
- Pull request #839 at d00beb9: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #876 at f92de76: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at 3ca0eb1: Blueprint/train car operations UI window
- Pull request #885 at d714b11: feat: Add notifications to Menu
- Pull request #886 at 6c0785b: Scene viewer extension to TrackViewer
- Pull request #892 at 1f5ba4c: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #903 at 29f3d1a: Downloading route content (Github, zip)
- Pull request #912 at f7b85e4: New Triple Valve Features Vol. 2
- Pull request #919 at 1a376fa: Added mouse wheel support for controls which can be moved by pressing t…
- Pull request #923 at e0f3c55: Add curve squeal to route
- Pull request #924 at 6c2c3cd: Default Asset Improvements
- Pull request #925 at e3b1688: Fix brakeshoe force bug
- Pull request #926 at b20ca94: Lights Bugfixes

Author: openrails-bot

Source/RunActivity/Viewer3D/Lights.cs

@@ -292,8 +292,8 @@ bool UpdateState()
             bool locomotiveFlipped = leadLocomotiveCar != null && leadLocomotiveCar.Flipped;
             bool locomotiveReverseCab = leadLocomotive != null && leadLocomotive.UsingRearCab;
             bool newCarIsReversed = Car.Flipped ^ locomotiveFlipped ^ locomotiveReverseCab;
-            bool newCarIsFirst = !Car.Lights.IgnoredConditions[1] && Car.Train == null || (locomotiveFlipped ^ locomotiveReverseCab ? Car.Train.LastCar : Car.Train.FirstCar) == Car;
-            bool newCarIsLast = !Car.Lights.IgnoredConditions[1] && Car.Train == null || (locomotiveFlipped ^ locomotiveReverseCab ? Car.Train.FirstCar : Car.Train.LastCar) == Car;
+            bool newCarIsFirst = !Car.Lights.IgnoredConditions[1] && (locomotiveFlipped ^ locomotiveReverseCab ? Car.Train?.LastCar : Car.Train?.FirstCar) == Car;
+            bool newCarIsLast = !Car.Lights.IgnoredConditions[1] && (locomotiveFlipped ^ locomotiveReverseCab ? Car.Train?.FirstCar : Car.Train?.LastCar) == Car;
             // Penalty
 			bool newPenalty = !Car.Lights.IgnoredConditions[2] && leadLocomotive != null && leadLocomotive.TrainBrakeController.EmergencyBraking;
             // Control