Fix keyboard tools script for anonymous users

app/assets/javascripts/keyboard_tools.js

 $(() => {
+    const userLink = $('.header--item.is-complex.is-visible-on-mobile[href^="/users/"]').attr('href');
+
     _CodidactKeyboard = {
         state: 'home',
         selectedItem: null,
-        user_id: parseInt($('.header--item.is-complex.is-visible-on-mobile[href^="/users/"]').attr('href').split("/").pop()),
+        user_id: !!userLink ? parseInt(userLink.split("/").pop(), 10) : null,
         is_mod: !!$('.header--item[href="/mod/flags"]').length,
         categories: function () {
             category_elements = $("a.category-header--tab");