mailbox_list_mailbox(): Don't show namespace prefix as selectable if it points to INBOX.
mailbox_list_mailbox(): Don't show namespace prefix as selectable if it points to INBOX.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot