`SceneRenderer` crashes when there is no material present

[wrestledBearOnce]

Example code

_scene = new SceneContainer
            {
                Children = new List<SceneNode>()
                {
                    new SceneNode
                    {
                        Components = new List<SceneComponent>
                        {
                            new Transform(),
                            new Cube()
                        }
                    }
                }
            };
_sceneRenderer = SceneRendererForward(_scene);

[...]

_sceneRenderer.Render(RC); // crash

Expected behavior

In the old days (tm) a default material got inserted. This behavior is now missing.

[wrestledBearOnce]

>	Fusee.Xene.dll!Fusee.Xene.VisitorCallerFactory.MakeComponentVisitor.AnonymousMethod__0(Fusee.Xene.Visitor<Fusee.Engine.Core.Scene.SceneNode, Fusee.Engine.Core.Scene.SceneComponent> visitor, Fusee.Engine.Core.Scene.SceneComponent component) Line 58	C#
 	Fusee.Xene.dll!Fusee.Xene.Visitor<Fusee.Engine.Core.Scene.SceneNode, Fusee.Engine.Core.Scene.SceneComponent>.DoVisitComponent(Fusee.Engine.Core.Scene.SceneComponent component) Line 590	C#
 	Fusee.Xene.dll!Fusee.Xene.Visitor<Fusee.Engine.Core.Scene.SceneNode, Fusee.Engine.Core.Scene.SceneComponent>.DoVisitComponents(Fusee.Engine.Core.Scene.SceneNode node) Line 563	C#
 	Fusee.Xene.dll!Fusee.Xene.Visitor<Fusee.Engine.Core.Scene.SceneNode, Fusee.Engine.Core.Scene.SceneComponent>.DoTraverse(Fusee.Engine.Core.Scene.SceneNode node) Line 541	C#
 	Fusee.Xene.dll!Fusee.Xene.Visitor<Fusee.Engine.Core.Scene.SceneNode, Fusee.Engine.Core.Scene.SceneComponent>.Traverse(System.Collections.Generic.IEnumerable<Fusee.Engine.Core.Scene.SceneNode> children) Line 155	C#
 	Fusee.Engine.Core.dll!Fusee.Engine.Core.SceneRendererForward.Render(Fusee.Engine.Core.RenderContext rc) Line 340	C#
 	Fusee.Examples.Simple.Core.dll!Fusee.Examples.Simple.Core.Simple.RenderAFrame() Line 151	C#
 	Fusee.Engine.Core.dll!Fusee.Engine.Core.RenderCanvas.InitApp.AnonymousMethod__36_5(object <p0>, Fusee.Engine.Common.RenderEventArgs <p1>) Line 221	C#
 	Fusee.Engine.Imp.Graphics.Desktop.dll!Fusee.Engine.Imp.Graphics.Desktop.RenderCanvasImpBase.DoRender() Line 552	C#
 	Fusee.Engine.Imp.Graphics.Desktop.dll!Fusee.Engine.Imp.Graphics.Desktop.RenderCanvasGameWindow.OnRenderFrame(OpenTK.Windowing.Common.FrameEventArgs args) Line 707	C#
 	OpenTK.Windowing.Desktop.dll!OpenTK.Windowing.Desktop.GameWindow.DispatchRenderFrame()	Unknown
 	OpenTK.Windowing.Desktop.dll!OpenTK.Windowing.Desktop.GameWindow.Run()	Unknown
 	Fusee.Engine.Imp.Graphics.Desktop.dll!Fusee.Engine.Imp.Graphics.Desktop.RenderCanvasImp.Run() Line 437	C#
 	Fusee.Engine.Core.dll!Fusee.Engine.Core.RenderCanvas.Run() Line 315	C#
 	Fusee.Examples.Simple.Desktop.dll!Fusee.Examples.Simple.Desktop.Simple.Main() Line 70	C#
 	[Native to Managed Transition]	
 	hostpolicy.dll!00007ff87cfc970b()	Unknown
 	hostpolicy.dll!00007ff87cfc9a3c()	Unknown
 	hostpolicy.dll!00007ff87cfca3d7()	Unknown
 	hostfxr.dll!00007ff885e7b589()	Unknown
 	hostfxr.dll!00007ff885e7e576()	Unknown
 	hostfxr.dll!00007ff885e808a1()	Unknown
 	hostfxr.dll!00007ff885e7ebd2()	Unknown
 	hostfxr.dll!00007ff885e782fb()	Unknown
 	Fusee.Examples.Simple.Desktop.exe!00007ff69c201f88()	Unknown
 	Fusee.Examples.Simple.Desktop.exe!00007ff69c2022fb()	Unknown
 	Fusee.Examples.Simple.Desktop.exe!00007ff69c2037a8()	Unknown
 	kernel32.dll!00007ff8df867034()	Unknown
 	ntdll.dll!00007ff8dfb42651()	Unknown