Non-replies cannot harvest parent notice nicknames

Non-replies cannot harvest parent notice nicknames

A feature we use of parent notices is that if you use the same @user
as the parent notice, the same @user will be notified, regardless if
there might be @user@site.com as well as @user@example.com and you're
subscribed to just one of them (or both, or none of them!).

But this threw an exception since we tested this on new notice threads.