fix window scroll handler leaks

[hkhere]

Related Issue

The window's scroll handler is not removed when a new scroll handler is to be installed.

This does not only leak handlers but also causes accumulated scroll handlers to be executed every time the scroll event is fired.

Your solution

remove current scroll handler when a new scroll handler is to be installed

[hkhere]

This can be easily verified using getEventListeners(window) in devtools and examine the scroll property of the output.