Includes:
* Checking if the directory exists and returning early otherwise.
* Removing a redundant `rmdir()` call in `clean_dirsize_cache()` tests.
Follow-up to [49744], [54300].
See #55652.
git-svn-id: https://develop.svn.wordpress.org/trunk@54303 602fd350-edb4-49c9-b593-d223f7449a82