I'm sometimes getting an invalid json reply from `getwalletinfo` when rescanning is in progress.

The invalid part is this: `"scanning":{"duration":19,"progress":}}` (no value for `progress`).

I can't reliably reproduce this, but I did manage to run into this 3 times now (once every 10-20 attempts or so).

I'm running v0.20.0 and testing against a regtest instance. This happens while doing a batched `importmulti` of 2000 addresses (none of which have history).
{
    for (const CTxIn& txin : tx->vin) {
        auto it = mapWallet.find(txin.prevout.hash);
        if (it != mapWallet.end()) {
            it->second.MarkDirty();
        }
    }
}
bool CWallet::AbandonTransaction(const uint256& hashTx)
{
    LOCK(cs_wallet);
    WalletBatch batch(*database);
    std::set<uint256> todo;
    std::set<uint256> done;
    
    auto it = mapWallet.find(hashTx);
    assert(it != mapWallet.end());
    CWalletTx& origtx = it->second;
    if (origtx.GetDepthInMainChain() != 0 || origtx.InMempool()) {
        return false;
    }
    todo.insert(hashTx);
    while (!todo.empty()) {
        uint256 now = *todo.begin();
        todo.erase(now);
        done.insert(now);