lib-storage: Open index with MAIL_INDEX_OPEN_FLAG_SAVEONLY if mailbox has MAILBOX_FLAG_SAVEONLY
lib-storage: Open index with MAIL_INDEX_OPEN_FLAG_SAVEONLY if mailbox has MAILBOX_FLAG_SAVEONLY

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