Only decrement the "update ahead" counter after Core::Render()

Only decrement the "update ahead" counter after Core::Render()

The issue:

Inside RenderThread::Run() it loops inside: while( mThreadSynchronization.RenderReady( request ) )
In normal usage mCore.Render() is called for each tick, before waiting again in ThreadSynchronization::RenderReady()
RenderReady() decrements mUpdateAheadOfRender, which counts how many frames ahead the update thread is (max of 2)
However in some scenario it skips the mCore.Render(), and still continues to decrement mUpdateAheadOfRender

The solution is to only decrement mUpdateAheadOfRender if Core::Render() has been called

Change-Id: I20dd3ad5b8055b7191397aa101aa5b88f632fe32