Fix zip download

Playground/zipContent/index.html

@@ -45,7 +45,7 @@
 ####INJECT####
 
         engine.runRenderLoop(function () {
-            if (sceneToRender) {
+            if (sceneToRender && sceneToRender.activeCamera) {
                 sceneToRender.render();
             }
         });