[BUGFIX] fluid: Harden CountViewHelper

The CountViewHelper calls count() on non-arrays or non-Countable
objects. This throws warnings on PHP 7.2 - sanitize this call.

Change-Id: Ie1932c31a099577cb0d344824a6441509aefbc03
Resolves: #83214
Releases: 7.6
Reviewed-on: https://review.typo3.org/54927


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