Sets @iter to point to the node following it at the current level.
If there is no next @iter, %FALSE is returned and @iter is set to be invalid.
the #GtkTreeIter-struct
Return: %TRUE if @iter has been changed to the next node
See Implementation
Sets @iter to point to the node following it at the current level.
If there is no next @iter, %FALSE is returned and @iter is set to be invalid.