static struct index_change *_find_change(struct mailbox *mailbox, uint32_t recno)
{
    uint32_t changeno = mailbox->index_change_map[recno % INDEX_MAP_SIZE];

    while (changeno) {
        if (mailbox->index_changes[changeno-1].record.recno == recno)
            return &mailbox->index_changes[changeno-1];
        changeno = mailbox->index_changes[changeno-1].mapnext;
    }

    return NULL;
}
static struct index_change *_find_change(struct mailbox *mailbox, uint32_t recno)
{
    uint32_t changeno = mailbox->index_change_map[recno % INDEX_MAP_SIZE];

    while (changeno) {
        if (mailbox->index_changes[changeno-1].record.recno == recno)
            return &mailbox->index_changes[changeno-1];
        changeno = mailbox->index_changes[changeno-1].mapnext;
    }

    return NULL;
}