Presenter view: notes appear one slide too early

Hi Jan-Erik,

nice work on the presenter view! I will give it a spin with my next talk...

I noticed that the presenter notes would appear one slide too early (you see the notes for the *next* slide in the presenter view).

Attached is a change to fix the behaviour. Please don't pull it in as is -- it's just a hack & only meant to demonstrate the problem.

Cheers,
Martin