Queue is cleared when new nodes are added to Infinite queue

When I've tried to add new nodes to queue (on page admin/content/nodequeue/.../view) using textfield 'Select title to add' and then submit it by 'Submit' button, all nodes were suddenly cleared from queue. I found that problem lies in nodequeue_arrange_subqueue_form_submit function, where nodequeue_check_subqueue_size is called and if queue size is 0 (infinite), queue is simply cleared. I suggest to check first if queue is infinite (in attached patch).