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

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

A gtk:tree-iter iterator if 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 iter. If the iterator was not set, nil is returned.