entryArea: Fix setting new nick immediately

The intended behavior when changing the nick via the popover is to update the button label immediately, and only revert to the actually used nick when the server doesn't react in a reasonable time (or simply rejects the update). However 911b9558 broke that, as the account's nickname property changes right away , but isn't actually used to set the nick label while connected. In that case the label is set from the connection's self-contact, which will only pick up the new nick after it changed on the server. So to avoid resetting the newly requested nick immediately, only consider changes to the nickname while disconnected.