docs: fix guard example (#3129)

* Update guard example to avoid stack overflow

* Update docs/guide/advanced/navigation-guards.md

Co-Authored-By: Eduardo San Martin Morote <posva@users.noreply.github.com>

* Use route name in next() call for consistency

Co-authored-by: Eduardo San Martin Morote <posva@users.noreply.github.com>

docs/guide/advanced/navigation-guards.md

@@ -39,7 +39,7 @@ Every guard function receives three arguments:
 ```js
 // BAD
 router.beforeEach((to, from, next) => {
-  if (!isAuthenticated) next('/login')
+  if (to.name !== 'Login' && !isAuthenticated) next({ name: 'Login' })
   // if the user is not authenticated, `next` is called twice
   next()
 })
@@ -48,7 +48,7 @@ router.beforeEach((to, from, next) => {
 ```js
 // GOOD
 router.beforeEach((to, from, next) => {
-  if (!isAuthenticated) next('/login')
+  if (to.name !== 'Login' && !isAuthenticated) next({ name: 'Login' })
   else next()
 })
 ```