Recreate the glfw window outside the key handler when switching to fullscreen mode

The window can't be deleted inside the event handler for the same window; this crashes sometimes on the mac.

Btw, this is not a regression from the latest changes; the original code handled two things in the event handler; exiting and switching to fullscreen. I also observed these crashes with Beta5.

Doing the `Init()` in the loop isn't elegant, but I don't know another way.