guard text.js node fetch on non-ok response

public/js/text.js

@@ -32,8 +32,15 @@ document.addEventListener('DOMContentLoaded', () => {
 
 function fetchAndRenderNodes(textId) {
     return fetch('/api/nodes/' + textId, { credentials: 'same-origin' })
-        .then(res => res.json())
+        .then(function (response) {
+            if (!response.ok) {
+                return null;
+            }
+            return response.json();
+        })
         .then(nodes => {
+            if (!Array.isArray(nodes)) return;
+
             const existing = document.querySelector('#text-detail > ul');
             if (existing) existing.remove();