Do not try to hide the splash screen twice
It's possible the splashscreen gets destroyed when it gets hidden,
which could cause the crash mentioned in issue #14. We set the splash
to None after we hide it as we don't need to retry hiding it after.
Add a 100ms timeout to the splash screen to allow it to show
Without it, the callback would get called before the splash screen
events got processed (such as Paint?) which will cause the splash
screen not to appear or to appear as a grey rectangle without the image
This could potentially fix issue #14