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).
{
    auto result = WITH_LOCK(g_loading_wallet_mutex, return g_loading_wallet_set.insert(name));
    if (!result.second) {
        error = Untranslated("Wallet already being loading.");
        status = DatabaseStatus::FAILED_LOAD;
        return nullptr;
    }
    auto wallet = LoadWalletInternal(chain, name, load_on_start, options, status, error, warnings);
    WITH_LOCK(g_loading_wallet_mutex, g_loading_wallet_set.erase(result.first));
    return wallet;
}
std::shared_ptr<CWallet> CreateWallet(interfaces::Chain& chain, const std::string& name, Optional<bool> load_on_start, DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error, std::vector<bilingual_str>& warnings)
{
    uint64_t wallet_creation_flags = options.create_flags;
    const SecureString& passphrase = options.create_passphrase;
    if (wallet_creation_flags & WALLET_FLAG_DESCRIPTORS) options.require_format = DatabaseFormat::SQLITE;
    
    bool create_blank = (wallet_creation_flags & WALLET_FLAG_BLANK_WALLET);
    
    if (!passphrase.empty()) {
        wallet_creation_flags |= WALLET_FLAG_BLANK_WALLET;
    }
    
    std::unique_ptr<WalletDatabase> database = MakeWalletDatabase(name, options, status, error);
    if (!database) {
        error = Untranslated("Wallet file verification failed.") + Untranslated(" ") + error;
        status = DatabaseStatus::FAILED_VERIFY;