Create a new iterator from an existing iterator. The new iterator
will only return those elements that match the given compare function func.
The first parameter that is passed to func is the GValue of the current
iterator element and the second parameter is user_data. func should
return 0 for elements that should be included in the filtered iterator.
When this iterator is freed, it will also be freed.
Create a new iterator from an existing iterator. The new iterator will only return those elements that match the given compare function func. The first parameter that is passed to func is the GValue of the current iterator element and the second parameter is user_data. func should return 0 for elements that should be included in the filtered iterator. When this iterator is freed, it will also be freed.