ZF-6765: Zend_Filter_Input::_validateRule() iterates through
provided fields when it's not necessary
Zend_Filter_Input::_validateRule() has the following code:   *
Evaluate the inputs against the validator chain. if
(count((array) $validatorRule[self::FIELDS]) > 1) { } else {
$failed = false;     foreach ($data as $fieldKey => $field) {
But $data cardinality is always less than (array)
$validatorRule[self::FIELDS] cardinality since $data elements
are collected by iterating through it.  It's not a bug, but it
reduces code readability ($data is always one element array).