[BUGFIX] EvaluteDisplayCondition should throw proper error message

When an extension author writes a display condition in TCA and
by incident uses a wrong format for the displayCondition (see ticket)
the strtoupper fails due to the lack of an associative array
because it's a numeric-key array.

An additional check fixes the issue.

Resolves: #79692
Releases: master, 8.7
Change-Id: I4455bdc908e0be1a373f86680e718e876aa5ddd7
Reviewed-on: https://review.typo3.org/58480


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>