Skip fly when in 2D Scene View

When in 2D scene view to edit a UI a warning is thrown. I have no idea if this is the best way to fix it, but it works and flying makes no sense in 2D so it works for me.

Fixes PatHightree#30

Editor/ViewportController.cs

@@ -132,6 +132,8 @@ static void Fly(SceneView sceneView)
 
         static void Fly(SceneView sceneView, Vector3 translationInversion, Vector3 rotationInversion)
         {
+            if (sceneView.in2DMode) return;
+
             SyncRigWithScene();
 
             // Apply inversion of axes for fly/grabmove mode.
@@ -433,4 +435,4 @@ private static Vector3 SnapOnTranslation(Vector3 v, float snap)
         #endregion - Snapping -
     }
 }
-#endif
+#endif