[php-src] Issue #7952: `CallbackFilterIterator` is not rewound by default/initialized

Issue: https://github.com/php/php-src/issues/7952 Comment Author: cmb69 This [issue is known for 14 years](https://bugs.php.net/bug.php?id=44063) (at least); I doubt that the behavior will change. I agree with @damianwadley that we should clearly document that iterators are supposed to be rewound before usage (although that is already implied by the [foreach example](https://www.php.net/manual/en/class.iterator.php)).