Description:
------------
PHP crashes when attempting to recreate a directory that already exists in an archive. yes it probably seems like bad practice to attempt to recreate a directory that already exists however, I found this while iterating through files/directories. the submitted code is the simpilest form in which the error can be reproduced.

Reproduce code:
---------------
<?php
// this code crashes php
$archive = new ZipArchive();
$archive->open('c:/test.zip', ZIPARCHIVE::CREATE);
$archive->addEmptyDir('test');
$archive->addEmptyDir('test');
?>

Expected result:
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the expected result would be for it to completely skip over the directory and or display a E_NOTICE that the directory already exists.

Actual result:
--------------
when attempting to create a directory that already exists in an archive, PHP crashes.