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.

The original patch was merged on September 12th here - https://github.com/joomla/joomla-cms/commit/341512fbc68f66daaeca3c4b4ae2d403b66a40dc - thankfully we haven't had a release since then...