[autocomplete] popup with transition flickers on input clear when searching for a non existent item

# Bug report

## Current behavior

Currently, when building an autocomplete with a transition provided to the popup, like the example below, the popup component flickers whenever you search for a non-existent item and then clear the input.

## Expected behavior

When the autocomplete input is cleared while searching for a non-existent item, the popup should close, and the list content shouldn't change during the closing transition timeframe.

## Reproducible example
_try searching for `z` and then deleting it:_
https://stackblitz.com/edit/vu1nb1hw?file=src%2FApp.tsx

## Base UI version

v1.3.0

## Which browser are you using?

Firefox

## Which OS are you using?

Mac OS