Automatic merge of T1.5.1-757-gef6c1a8c8 and 17 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 #874 at f8dbeab: Dynamic brake controller refactoring
- Pull request #875 at 43bf33e: Bug fix for https://bugs.launchpad.net/or/+bug/2036346 Player train switching doesn't work with 3D cabs
- Pull request #876 at f92de76: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at 356b543: Blueprint/train car operations UI window
- Pull request #885 at c81447b: feat: Add notifications to Menu
- Pull request #886 at 685315b: Scene viewer extension to TrackViewer
- Pull request #888 at d7daf62: docs: Document player application model
- Pull request #890 at 39a9fa4: Allow depart early
- Pull request #892 at 1f5ba4c: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #893 at bf8876b: Signal errors
- Pull request #894 at 794fddf: Correct Decrease Colour
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #897 at 0a9d939: feat: Improved system information collection
- Pull request #898 at e271395: Extra line with all the arguments for debugging purposes in logfile
- Pull request #900 at 42ea7ad: DMI updates

Source/RunActivity/Viewer3D/Popups/TrainCarOperationsWindow.cs

@@ -504,6 +504,7 @@ public override void PrepareFrame(ElapsedTime elapsedTime, bool updateFull)
             {
                 var trainCarViewer = Owner.Viewer.TrainCarOperationsViewerWindow;
                 var carOperations = Owner.Viewer.CarOperationsWindow;
+                var trainCarWebpage = Owner.Viewer.TrainCarOperationsWebpage;
 
                 trainCarViewer.TrainCarOperationsChanged = !trainCarViewer.Visible && trainCarViewer.TrainCarOperationsChanged ? false : trainCarViewer.TrainCarOperationsChanged;
 
@@ -577,7 +578,7 @@ public override void PrepareFrame(ElapsedTime elapsedTime, bool updateFull)
                     carOperations.CarOperationChanged = carOperations.Visible && carOperations.CarOperationChanged;
                 }
 
-                if (CarPosition != trainCarViewer.CarPosition && Owner.Viewer.TrainCarOperationsWebpage.Connections > 0)
+                if (trainCarWebpage != null && CarPosition != trainCarViewer.CarPosition && trainCarWebpage.Connections > 0)
                 {
                     // Required to scroll the main window from the web version
                     UpdateTrainCarOperation = true;