[BUGFIX] Upgrade wizard crashes if never updated before

If the array $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['ext/install']
is not set, the upgrade wizard crashes.

Resolves: #72435
Releases: master
Change-Id: Ibb794972917ff5aa0934af7ad88fdfb609e72a8e
Reviewed-on: https://review.typo3.org/45438


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>