ensure current_limit exist before displaying any message based on it

ihatemoney/web.py

@@ -192,8 +192,10 @@ def admin():
             session["is_admin"] = True
             session.update()
             return redirect(goto)
+        if limiter.current_limit is not None:
             msg = _(
                 "This admin password is not the right one. Only %(num)d attempts left.",
+                # If the limiter is disabled, there is no current limit
                 num=limiter.current_limit.remaining,
             )
             form["admin_password"].errors = [msg]