Fix missing initializer for NullHandleRef

[micdenny]

fixes #2

[cpuwzd]

I'm sorry that I wasn't more involved in this fix. I hadn't forked your project, so a pull request would have been awkward, especially for such a simple change. I was just using your code for reference and reporting a compilation error picked up by one of Microsoft's wizards.

[micdenny]

Yes in fact was super easy, thank you