imapc: Don't crash when trying to use imapc's subscription list for another namespace.
imapc: Don't crash when trying to use imapc's subscription list for another namespace.

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