fix NullReferenceExceptions with focused boids during maximized play

during maximized play, focusing a Boid would cause NullReferenceExceptions as there was no active SceneView in the Unity Editor. Thus, without a SceneView, attempting to acquire one would return null. No test was done prior to acting on the Nullable return.

Boids/Assets/Scripts/BoidController.cs

@@ -75,7 +75,7 @@ public class BoidController : MonoBehaviour {
         
         // Focus on the boid in scene view when one is focused
         #if UNITY_EDITOR
-        if(focusedBoid != null)
+        if(focusedBoid != null && SceneView.lastActiveSceneView != null)
             SceneView.lastActiveSceneView.LookAtDirect(focusedBoid.transform.position, Quaternion.identity);
         #endif
     }