doveadm backup: Fix to earlier commit - don't try to delete an already empty mailbox.
doveadm backup: Fix to earlier commit - don't try to delete an already empty mailbox.

jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch