Admin users are not allowed for a project

In function isUserAllowed() it is only checked if:
1. any user is assigned to the project (if no then allow anybody)
2. if logged user is allowed for given project
But also _admin_ users _not assigned_ to the project shall be allowed.

models/project.php

@@ -82,6 +82,15 @@ class Project extends Base
 
         if ($nb_users < 1) return true;
 
+        // check if user has admin rights
+        $nb_users = $this->db
+                    ->table(\Model\User::TABLE)
+                    ->eq('id', $user_id)
+                    ->eq('is_admin', 1)
+                    ->count();
+         
+        if ($nb_users > 0) return true;
+
         // Otherwise, allow only specific users
         return (bool) $this->db
                     ->table(self::TABLE_USERS)