DirectionalLightShadowRenderer: fix debugFrustum

Author: capdevon

jme3-core/src/main/java/com/jme3/shadow/DirectionalLightShadowRenderer.java

@@ -212,9 +212,9 @@ protected Camera getShadowCam(int shadowMapIndex) {
 
     @Override
     protected void doDisplayFrustumDebug(int shadowMapIndex) {
-        ((Node) viewPort.getScenes().get(0)).attachChild(createFrustum(points, shadowMapIndex));
+        getMainScene().attachChild(createFrustum(points, shadowMapIndex));
         ShadowUtil.updateFrustumPoints2(shadowCam, points);
-        ((Node) viewPort.getScenes().get(0)).attachChild(createFrustum(points, shadowMapIndex));
+        getMainScene().attachChild(createFrustum(points, shadowMapIndex));
     }
 
     @Override