fix(Examples): prevent crash on scene change with active arrow

When the arrow prefab had collided with something it would re-enable
the interactable object on the arrow causing a chain of events that
could cause a crash if the scene was being changed at the point
this was initiated.

This fix checks to make sure the arrow is still active before trying
to reset it.

Assets/VRTK/Examples/ExampleResources/Scripts/Archery/Arrow.cs

@@ -63,7 +63,7 @@ private void FixedUpdate()
 
         private void OnCollisionEnter(Collision collision)
         {
-            if (inFlight)
+            if (inFlight && isActiveAndEnabled && gameObject.activeInHierarchy)
             {
                 ResetArrow();
             }