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.