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).
unsigned int limit_ancestor_count = 0;
    unsigned int limit_descendant_count = 0;
    chain().getPackageLimits(limit_ancestor_count, limit_descendant_count);
    size_t max_ancestors = (size_t)std::max<int64_t>(1, limit_ancestor_count);
    size_t max_descendants = (size_t)std::max<int64_t>(1, limit_descendant_count);
    bool fRejectLongChains = gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS);
    
    
    if (coin_control.m_avoid_partial_spends && vCoins.size() > OUTPUT_GROUP_MAX_ENTRIES) {
        
        
        
        Shuffle(vCoins.begin(), vCoins.end(), FastRandomContext());
    }
    std::vector<OutputGroup> groups = GroupOutputs(vCoins, !coin_control.m_avoid_partial_spends, max_ancestors);
    bool res = value_to_select <= 0 ||
        SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 6, 0), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used) ||
        SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 1, 0), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used) ||
        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, 2), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
        (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
        (m_spend_zero_conf_change && !fRejectLongChains && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max()), groups, setCoinsRet, nValueRet, coin_selection_params, bnb_used));
    
    util::insert(setCoinsRet, setPresetCoins);
    
    nValueRet += nValueFromPresetInputs;
    return res;
}
bool CWallet::SignTransaction(CMutableTransaction& tx) const