ResizeSensor kills performance when meets with a Window type

[kergekacsa]

Hi there!

I've found an infinit loop in this line: (at https://github.com/marcj/css-element-queries/blob/master/src/ResizeSensor.js#L239 )
var invisible = element.offsetWidth === 0 && element.offsetHeight === 0;

The problem is that Windows types doesn't have offsetWidth/offsetHeight, so it's basically redraw the whole layout again and again.
It would be a nice touch if in case os a Window type if could use a little smarter check for invisibility. I've think something like this:
https://gist.github.com/danbrianwhite/bcdd7fbd6d775a4e0dc0

What do you think?