Hi,

When dropdown shown above input and you start searching some term, the list of items starts getting reduced and instead of the the menu resizing down when rows are hidden, divs are hidden/removed but their place is still there and you can see through it until you scroll the page just a bit and then it renders and the menu gets resized and the spaces where the hidden rows once where get removed also.

This issue is occurring with select 4.0.0 all the way to 4.0.9 on Mac with the following browsers: Chrome, Safari, Firefox, on Win 7/10 IE11/Edge.

The screenshot above was created on https://select2.org/getting-started/basic-usage
Steps to reproduce:

• visit https://select2.org/getting-started/basic-usage
• resize your browser so one of the select2 inputs it right at the bottom of the screen and click on the menu for it to open above input
• start searching and you will notice the empty space where the div once were but the menu doesn't shrink/resize

This issue is only when menu is above input, anytime it's below input menu resizes correctly.