If user not logged in redirect to base path (#445)

Solved problem when  user not logged in can go to admin/something and view admin dashboard with Error 404.

admin.php

@@ -374,6 +374,7 @@ class AdminPlugin extends Plugin
         };
 
         if (empty($this->grav['page'])) {
+            if($this->session->user->count()){
                 $event = $this->grav->fireEvent('onPageNotFound');
 
                 if (isset($event->page)) {
@@ -382,6 +383,9 @@ class AdminPlugin extends Plugin
                 } else {
                     throw new \RuntimeException('Page Not Found', 404);
                 }
+            }else{
+                $this->grav->redirect($this->base);
+            }
         }
 
         // Explicitly set a timestamp on assets