Installer fails when recursively deleting a folder on BSD

[Vringe]

We have some customers complaining about failing installations of Woltlab Suite. (Also tested on Core)

It looks like a problem related to BSD and NFS environments. It's a fundamental issue, which was discussed here a long time ago: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=57696#c14 https://forums.freebsd.org/threads/problem-wiith-removing-folders-on-nfs.82034/#post-531210

This is also kind of mentioned in the POSIX spec:

If a file is removed from or added to the directory after the most recent call to opendir() or rewinddir(), whether a subsequent call to readdir() returns an entry for that file is unspecified.

It fails when the installer tries to delete tmp files: https://github.com/WoltLab/WCF/blob/master/wcfsetup/install/files/lib/system/WCFSetup.class.php#L1072

I was able to implement a workaround by filling the iterator items into an array:

                 ),
                 \RecursiveIteratorIterator::CHILD_FIRST
             );
+             $tmpDirectoryIterator = iterator_to_array($tmpDirectoryIterator);
             foreach ($tmpDirectoryIterator as $tmpFile) {
                 if ($tmpFile->isDir()) {
                     \rmdir($tmpFile);

This may lead to out-of-memory situations depending on how many files there are. An other approach would be to get 20 files, delete them, and then get another 20 until the folder is empty.