[BUGFIX] Allow redirect from typo3/install again

Due to refactorings of constants, Environment:isCli()
needs to be initialized now. This breaks the
existing redirect from typo3/install/ to
typo3/install.php, due to non-initialized Environment
API.

In this case, the environment is initialized.

Resolves: #85306
Releases: master
Change-Id: I20a86f4a304951b7b075a3eec7142c4e1c99d06c
Reviewed-on: https://review.typo3.org/57262


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>