[EuiComboBox] Options list doesn't show when singleSelection and onCreateOption are set

[yuliacech]

Hi team,

I noticed an issue with the combo box options list not being shown when the user clicks inside the input field. The list will show eventually when the user starts typing the value in the input or if they click the "arrow down" icon on the right. I think that only happens when both props are set: singleSelection={{ asPlainText: true }} and onCreateOption.
Here is a minimal reproducible example: https://codesandbox.io/s/combobox-example-7bw9r?file=/index.js:442-481

Expected behaviour: the options list is shown when the user clicks inside the input field without having to type in any value. The same it works with singleSelection={false}

Here are 2 gifs to demonstrate: