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).
{
    
    bool result = true;
    for (const auto& spk_man : GetActiveScriptPubKeyMans()) {
        result &= spk_man->IsHDEnabled();
    }
    return result;
}
bool CWallet::CanGetAddresses(bool internal) const
{
    LOCK(cs_wallet);
    if (m_spk_managers.empty()) return false;
    for (OutputType t : OUTPUT_TYPES) {
        auto spk_man = GetScriptPubKeyMan(t, internal);
        if (spk_man && spk_man->CanGetAddresses(internal)) {
            return true;
        }
    }
    return false;
}
void CWallet::SetWalletFlag(uint64_t flags)