Added Scene::GetActiveCamera()

Also fixed a warning when instancing is used without lighting


Former-commit-id: 5326e95f99a58ffcc91d7942ec2991482d7e58bd

include/Nazara/3D/Scene.hpp

@@ -34,6 +34,7 @@ class NAZARA_API NzScene
 		void Cull();
 		void Draw();
 
+		const NzCamera* GetActiveCamera() const;
 		NzBackground* GetBackground() const;
 		NzSceneNode& GetRoot() const;
 		float GetUpdateTime() const;