[BUGFIX] Incomplete mocks in fluid tests

Sanitize some view helper unit tests to not trigger
PHP 7.2 warnings count()'ing non-arrays by proper mocking.

Change-Id: I9929a02a03c9218ab73838f4a214165333d414aa
Resolves: #83213
Releases: 7.6
Reviewed-on: https://review.typo3.org/54926


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>