After login, redirect to the original URL called

Fix an annoying issue in Admin, when loading an inner page
(`/admin/pages/whatever`) and I'm logged out, after login I'm always
sent to the dashboard, while it should bring to the page I called in
the first place

classes/admin.php

@@ -185,8 +185,7 @@ class Admin
                     $grav = $this->grav;
 
                     $this->setMessage($this->translate('PLUGIN_ADMIN.LOGIN_LOGGED_IN'), 'info');
-                    $redirect_route = $this->uri->route();
-                    $grav->redirect($redirect_route);
+                    $grav->redirect($form['redirect']);
                 }
             }
         }

themes/grav/templates/partials/login.html.twig

@@ -14,7 +14,7 @@
         <form method="post" action="{{ base_url_relative }}">
             <div class="padding">
                 {% block form %}{% endblock %}
-
+                <input type="hidden" name="redirect" value="{{ uri.url }}" />
                 {{ nonce_field('admin-form', 'admin-nonce') }}
             </div>
         </form>