[BUGFIX] Ensure UserAspect->isLoggedIn() checks for user only

isLoggedIn() is referring to the user, as Frontend sometimes needs
"isUserOrGroupSet()" functionality for working with Admin Panel Previews
or the infamous pages.fe_login_mode where the user log in is hidden but
the group is still valid.

Resolves: #90989
Releases: master, 10.4
Change-Id: Ib19dfbea6c355abe51507430fb03e247eb5c27bf
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64441


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Reviewed-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>