[useScrollTrigger] Do nothing if target is null

[vipierozan99]

Currently if options.target is undefined it tried to default to the window.

In my case I have another component that may or may not be mounted at a given time, so the ref to it might be null.

Right now I do:

const isScrolled = useScrollTrigger({
  target: containerRef.current ?? undefined,
  threshold: 1,
});

but that will default to the window, and if its not present it will throw an error. Which is not what I want exactly.

This change just disables the hook if null is explicitly passed.