You can't have anonymous functions in 5.2

This PR was originally to fix the `E_DEPRECATED` that was thrown do to our usage of the `e` modifier in the `JFilterInput::_decode` method, but I saw that a fix for it has been merged. However, this fix utilizes anonymous functions, something that doesn't exist in PHP 5.2. Since Joomla 2.5 has a minimum requirement of 5.2, we cannot use anonymous functions in this case.