[FE] Fallback to /root node of a sitemap when a node is not found

Issue occurs when user has a document that is not an XPage opened in a channel preview and tries to open a sitemap. Sitemap behaves in the way that it tries to expand to the current shown page as a selected node, but if it's a document, there is no node for it so a 400 error is thrown on sitemap load.

Proposed solution: fall back to / if a range of 400 error is thrown.