refac: has_users

Co-Authored-By: pickle-dice <159401444+hassan-ajek@users.noreply.github.com>

backend/open_webui/models/users.py

@@ -258,6 +258,10 @@ class UsersTable:
         with get_db() as db:
             return db.query(User).count()
 
+    def has_users(self) -> bool:
+        with get_db() as db:
+            return db.query(db.query(User).exists()).scalar()
+
     def get_first_user(self) -> UserModel:
         try:
             with get_db() as db: