[BUGFIX] Check if TypoScript is loaded for indexed_search

Check if TypoScript is loaded for indexed_search, if not,
show an error message.

Resolves: #75866
Releases: master, 7.6
Change-Id: I0b5be9d959dd0d4fc4a5f4df1b287c4a0fca2885
Reviewed-on: https://review.typo3.org/49812


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Tomasz Stępniak <stempl88@gmail.com>
Reviewed-by: Michał Jankiewicz <michal.jankiewicz@gmail.com>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>