[BUGFIX] Avoid unnecessary I/O in GeneralUtility::createVersionNumberedFilename()

With this commit we prevent to check for existence of file
when we don't need to, because mode is not either 'embed' or
'querystring'

Resolves: #82565
Releases: master, 8.7
Change-Id: I829b8e87d951a6f170bc03d8b7836f671b51bdf4
Reviewed-on: https://review.typo3.org/54221


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anders Kostending <aha@systime.dk>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Wolfgang Klinger <wolfgang@wazum.com>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>