[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.

Fixes: #82969
Releases: master, 8.7, 7.6
Change-Id: If2827902443ff7411d9b2c1050213be3e0d78fb6
Reviewed-on: https://review.typo3.org/54694


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>