[BUGFIX] Only throw EM Offline Exception when EM is offline

Since #66597 the EM can be set offline. The value is checked in
TerUtility and Helper, but in TerUtility it's done wrong and leads to
a misleading error "Extension Manager is in offline mode"
which is not true

Resolves: #68331
Releases: master
Change-Id: Iee55c95a3d43250f43c8fef506a6884b75674504
Reviewed-on: http://review.typo3.org/41657


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Markus Sommer <markussom@posteo.de>
Tested-by: Markus Sommer <markussom@posteo.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>