Add NavMesh Modifier Volume actor type

Source/Editor/SceneGraph/SceneGraphFactory.cs

@@ -62,6 +62,7 @@ namespace FlaxEditor.SceneGraph
             CustomNodesTypes.Add(typeof(NavMeshBoundsVolume), typeof(NavMeshBoundsVolumeNode));
             CustomNodesTypes.Add(typeof(BoxVolume), typeof(BoxVolumeNode));
             CustomNodesTypes.Add(typeof(NavLink), typeof(NavLinkNode));
+            CustomNodesTypes.Add(typeof(NavModifierVolume), typeof(NavModifierVolumeNode));
             CustomNodesTypes.Add(typeof(ParticleEffect), typeof(ParticleEffectNode));
             CustomNodesTypes.Add(typeof(SceneAnimationPlayer), typeof(SceneAnimationPlayerNode));
         }