[TASK] Properly check for HTTPS

Take into account empty and "off" values for the HTTPS request variable
to support ISAPI with IIS.

Resolves: #81837
Releases: master, 8.7
Change-Id: I5937c506d3e36a2009a8da6e66724728654b4001
Reviewed-on: https://review.typo3.org/55750


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>