Adding null check for the rendering handler thread

[pritamps]

This will prevent the app from crashing if the rendering thread is null when the loading is complete

[babramovitch]

This won't fix the problem, it will just crash a couple lines down when it attempts to access the looper

renderingHandler = new RenderingHandler(renderingHandlerThread.getLooper(), this);

[jlo1]

This PR #824 should fix the issue.

[pritamps]

Good point about the issue just being pushed further down with my attempted fix... And Thanks to @jlo1 for pointing out a fix to the actual issue!