When the admin panel is active, the rendered page should always
be marked as "preview mode" so TSFE will later set
TSFE->no_cache which then allows to not store anything
in the Page cache.

Resolves: #92242
Releases: master, 10.4, 9.5
Change-Id: I6ef326d0a65b3b2c0dfdec7bf2bc29831c267b10
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66156


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Sybille Peters <sypets@gmx.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>