UI: CJ state can get messed up in some flows

[kxcd]

Re-posting from the Discord, the issue appears to be with Start CoinJoin button on the Core QT Desktop wallet.

Something small for the Dash Core Qt wallet: With coinjoin already enabled (unlocked for coinjoin), fully unlocking the wallet and then re-locking it will disable coinjoin, but the interface shows it is still active, making the user think it is still working, yet no mixing takes place. The button must be pushed to stop coinjoin (even though it's already stopped) and then start it again.

Discord link: https://discord.com/channels/484546513507188745/614505310593351735/1421937663455527054