Two admins in one group chat shared one draft and one wizard step: clientDrafts and userStateStore were keyed by chat id alone, so the second admin's wizard opened on the first one's email and limits, and whichever of them tapped a control last decided what the other created.
Key both stores by (chat, user) instead. A private chat is unaffected: its two ids are equal, so the key matches what the chat alone used to be. A message with no sender (a channel post) keys to user 0, which no admin holds.
Fixes#6593.