mailbox_list_get_unexpanded_path(): Don't crash with -o mail_location=..
mailbox_list_get_unexpanded_path(): Don't crash with -o mail_location=..

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