Fix for autoplay=false

If you set autoplay to false, it will still auto play anyway, because
promise chains like this still execute even when you don't return a
promise from the execute call. This fix means that we call play only if
autoplay is true and after the load promise is complete.
I think that an else case needs to be added to return load.promise
Otherwise, it look to me that callers of load with autoPlay === false will get a promise that completes on initialization not on load.