[BUGFIX] Possible string argument for uksort_recursive()

Follow-up: 24fcb06ec85fb78b2d1945d238152f6cc085f6f2
Change-Id: I8e7300b1c215bcc343399dc22a61cb1aa62b72cb
Reviewed-on: http://review.typo3.org/31852
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>