Fixed 404 when no lastPage was stored (solves #189)

Co-authored-by: Adam Bem <adam.bem@zoho.eu>
Reviewed-on: #190

Frontend/assets/scripts/frame.js

@@ -107,7 +107,11 @@ function changeTool(tool) {
  * @returns {void}
  */
 function loadLastPage() {
-    const lastPage = localStorage.getItem("lastPage");
+    var lastPage = localStorage.getItem("lastPage");
+    if (lastPage == null) {
+        lastPage = "xpath";
+    }
+
     switch (lastPage) { // XML category is default.
         case "jsonform":
             changeActiveTools('JSON');