bugfix #960: Verify project menu element existance before using them

src/scripts/navigate-event.js

@@ -62,8 +62,10 @@ document.addEventListener("DOMContentLoaded", function() {
         document.querySelector('solid-route[name="admin-projects"]').setAttribute('active','');
         document.querySelector('.jsRightMenu solid-link[next="admin-projects"]').setAttribute('active','');
       } else {
-        document.querySelector('solid-route[name="admin-projects"]').removeAttribute('active');
-        document.querySelector('.jsRightMenu solid-link[next="admin-projects"]').removeAttribute('active');
+        let adminProjects = document.querySelector('solid-route[name="admin-projects"]');
+        let rightMenu = document.querySelector('.jsRightMenu solid-link[next="admin-projects"]');
+        if( adminProjects ) adminProjects.removeAttribute('active');
+        if( rightMenu ) rightMenu.removeAttribute('active');
       }
       closeLeftMenu();
       closeUserControls();
@@ -124,4 +126,4 @@ document.addEventListener("DOMContentLoaded", function() {
         });
       }
     );
-});
\ No newline at end of file
+});