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).
if (mine == ISMINE_NO) {
                continue;
            }
            if (!allow_used_addresses && IsSpentKey(wtxid, i)) {
                continue;
            }
            std::unique_ptr<SigningProvider> provider = GetSolvingProvider(wtx.tx->vout[i].scriptPubKey);
            bool solvable = provider ? IsSolvable(*provider, wtx.tx->vout[i].scriptPubKey) : false;
            bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
            vCoins.push_back(COutput(&wtx, i, nDepth, spendable, solvable, safeTx, (coinControl && coinControl->fAllowWatchOnly)));
            
            if (nMinimumSumAmount != MAX_MONEY) {
                nTotal += wtx.tx->vout[i].nValue;
                if (nTotal >= nMinimumSumAmount) {
                    return;
                }
            }
            
            if (nMaximumCount > 0 && vCoins.size() >= nMaximumCount) {
                return;
            }
        }
    }
}
std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins() const
{
    AssertLockHeld(cs_wallet);
    std::map<CTxDestination, std::vector<COutput>> result;
    std::vector<COutput> availableCoins;
    AvailableCoins(availableCoins);