gtk-tree-model-filter-convert-child-iter-to-iter (filter child-iter)

filter -- a gtk-tree-model-filter object
child-iter -- a valid gtk-tree-iter iterator pointing to a row on the child model

A gtk-tree-iter iterator if child-iter is a valid iterator pointing to a visible row in child model.

Returns an interator to point to the row in filter that corresponds to the row pointed at by child-iter. If the iterator was not set, nil is returned.