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).
{
    std::vector<bilingual_str> warnings;
    return RemoveWallet(wallet, load_on_start, warnings);
}
std::vector<std::shared_ptr<CWallet>> GetWallets()
{
    LOCK(cs_wallets);
    return vpwallets;
}
std::shared_ptr<CWallet> GetWallet(const std::string& name)
{
    LOCK(cs_wallets);
    for (const std::shared_ptr<CWallet>& wallet : vpwallets) {
        if (wallet->GetName() == name) return wallet;
    }
    return nullptr;
}
std::unique_ptr<interfaces::Handler> HandleLoadWallet(LoadWalletFn load_wallet)