Fall back to using `window`, when the querySelector for scrollContainer returns null

I have a problem in my app where when unloading a page a loading another one I pass the ID of my own `scrollContainer` but that scroll container element only exists in the unloading page, but not in the page that is currently loading.
Problem is that react-lazy load executes a `scrollport.document.querySelector(scrollContainer)` which returns `null`, hence crashes.
My suggestion is to default back to the `window` element if the `querySelector` returns `null`

This line:
`scrollport = scrollport.document.querySelector(scrollContainer);`
would become this:
`scrollport = scrollport.document.querySelector(scrollContainer) || window;`