Sets @iter to be the child of @parent, using the given index.
The first index is 0. If @n is too big, or @parent has no children,
@iter is set to an invalid iterator and %FALSE is returned. @parent
will remain a valid node after this function has been called. As a
special case, if @parent is %NULL, then the @n-th root node
is set.
Sets @iter to be the child of @parent, using the given index.
The first index is 0. If @n is too big, or @parent has no children, @iter is set to an invalid iterator and %FALSE is returned. @parent will remain a valid node after this function has been called. As a special case, if @parent is %NULL, then the @n-th root node is set.