When I run `scantxoutset` via RPC using big range (e.g. 10000) on XPUB, the progress report indicator (`scantxoutset status`) reports 100% at start (while the keys are being derived). This is most probably the result of the previous operation. The progress is only reset to zero when the actual scan starts. I would expect the progress is set to zero before the keys are being derived.

Output of periodic calls to `scantxoutset status` while performing long operation.

```
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 100 }
{ progress: 0 }
{ progress: 3 }
{ progress: 6 }
{ progress: 9 }
{ progress: 12 }
{ progress: 15 }
{ progress: 17 }
{ progress: 20 }
{ progress: 23 }
{ progress: 26 }
{ progress: 29 }
{ progress: 32 }
{ progress: 35 }
{ progress: 37 }
{ progress: 40 }
{ progress: 43 }
{ progress: 46 }
{ progress: 49 }
{ progress: 51 }
{ progress: 54 }
{ progress: 57 }
{ progress: 60 }
{ progress: 63 }
{ progress: 66 }
{ progress: 68 }
{ progress: 71 }
{ progress: 74 }
{ progress: 77 }
{ progress: 80 }
{ progress: 82 }
{ progress: 85 }
{ progress: 88 }
{ progress: 91 }
{ progress: 94 }
{ progress: 97 }
{ progress: 100 }
```
CChain& active_chain = chainman.ActiveChain();
    /*
     * Idea: The set of chain tips is the active chain tip, plus orphan blocks which do not have another orphan building off of them.
     * Algorithm:
     *  - Make one pass through BlockIndex(), picking out the orphan blocks, and also storing a set of the orphan block's pprev pointers.
     *  - Iterate through the orphan blocks. If the block isn't pointed to by another orphan, it is a chain tip.
     *  - Add the active chain tip
     */
    std::set<const CBlockIndex*, CompareBlocksByHeight> setTips;
    std::set<const CBlockIndex*> setOrphans;
    std::set<const CBlockIndex*> setPrevs;
    for (const std::pair<const uint256, CBlockIndex*>& item : chainman.BlockIndex()) {
        if (!active_chain.Contains(item.second)) {
            setOrphans.insert(item.second);
            setPrevs.insert(item.second->pprev);
        }
    }
    for (std::set<const CBlockIndex*>::iterator it = setOrphans.begin(); it != setOrphans.end(); ++it) {
        if (setPrevs.erase(*it) == 0) {
            setTips.insert(*it);
        }
    }
    
    setTips.insert(active_chain.Tip());
    
    UniValue res(UniValue::VARR);
    for (const CBlockIndex* block : setTips) {
        UniValue obj(UniValue::VOBJ);
        obj.pushKV("height", block->nHeight);
        obj.pushKV("hash", block->phashBlock->GetHex());