Fix list of displayed nodes in Node Selection Window

Only the root node was displayed, instead of the whole hierarchy.
Bug introduced in commit c6f79866.

src/interface/Node_select.cpp

@@ -168,7 +168,9 @@ void Node_select::set_container_names_rec(QTreeWidgetItem *current_node, Contain
         children = current_container->get_view_children();
     }
 
-    if( (load_view == false) || (children == NULL)) {
+    /* children cannot be NULL when accessed, because it means load_view==true
+     * and thus, children was assigned in the above condition block. */
+    if(load_view==false || children->empty()) {
         children = current_container->get_children();
     }