[BUGFIX] Only count items in ForViewHelper when ``iteration`` argument is set
When using the ``iteration`` argument, the ``ForViewHelper`` provides
information about the current iteration, including the ``cycle`` and
``total``. Therefore it needs to count all elements.
The problem is, that this happens even if the iteration argument is
not specified leading to performance issues especially when iterating
over a (subset of a) lot of (remote) items.
This patch fixes this by adding a check for the ``iteration`` argument.
Releases: master, 3.0, 2.3, 2.2, 2.1