Previous slot’s firestone is lost when rollback.

[HarvestStars]

There is a scene in which the firestone disappears into view.

Environment:
lavad version v0.3.4.

details:
At the end of slot N-1, Alice buys a firestone(marked as F, the transaction is T), so that the firestone F could be usable in slot N. However, the blockchain rolls back at this moment, leading to the transaction T is packed in slot N.
Then, T migrates from slot N-1 to slot N, and F is lost in our rpc of listfirestone

code
here is the problem code

bool TestTicket(const int height, const CTicketRef ticket)
{
    auto index = pticketview->SlotIndex();
    auto len = pticketview->SlotLength();
    if (ticket->LockTime() != ((index + 1) * len -1)) {
        return false;
    }
    if (ticket->nValue != pticketview->CurrentTicketPrice()) {
        return false;
    }
    return true;
}