[BUGFIX] Prevent javascript error in backend

Adding a condition to check if a backend user has permissions on the
search to prevent a JS error while initializing the autocomplete module.
Also check if a module is available to start with.

Fixes: #82969
Releases: master, 8.7, 7.6
Change-Id: If2827902443ff7411d9b2c1050213be3e0d78fb6
Reviewed-on: https://review.typo3.org/54714


Reviewed-by: Markus Günther <mail@markus-guenther.de>
Tested-by: Markus Günther <mail@markus-guenther.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Henning Liebe <h.liebe@neusta.de>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>