Don't query for admin if user id is none

src/data_storage.py

@@ -54,7 +54,9 @@ def get_user_id_if_email_exists(email: str) -> int | None:
     return user_id
 
 
-def is_admin(user_id: int):
+def is_admin(user_id: int | None):
+    if user_id is None:
+        return False
     query_result = supabase_client.table(USERS_TABLE).select("admin").eq("user_id", user_id).execute().data
     if query_result:
         return query_result[0]["admin"] is True