app: fixed error setting page title based on non-existing header

js/erp5_loader.js

@@ -3241,13 +3241,12 @@
         $.i18n.setLng(new_language, function () {
           map.actions.translateNodeList(document);
 
-          // also translate page header
-          lookup = util.getHeader()
-            .getElementsByTagName("H1")[0]
-            .getAttribute("data-i18n");
+          // also translate page header, if there is one
+          lookup = util.getHeader().getElementsByTagName("H1")[0];
 
           if (lookup) {
-            document.title = map.actions.translateLookup(lookup);
+            document.title =
+              map.actions.translateLookup(lookup.getAttribute("data-i18n"));
           }
         });
       }