[BUGFIX] Unset current file in generic Content Object Renderer

When function is done, reset current file for further processing

Resolves: #77645
Releases: master, 8.7, 7.6
Change-Id: Ibae2e3221c51c8cb45f92b0bc7dbe395cc809605
Reviewed-on: https://review.typo3.org/49616


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benjamin Serfhos <serfhos@gmail.com>
Tested-by: Benjamin Serfhos <serfhos@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Elmar Hinz <t3elmar@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>