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 (IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
        return nullptr;
    }
    
    
    auto it = m_internal_spk_managers.find(OutputType::LEGACY);
    if (it == m_internal_spk_managers.end()) return nullptr;
    return dynamic_cast<LegacyScriptPubKeyMan*>(it->second);
}
LegacyScriptPubKeyMan* CWallet::GetOrCreateLegacyScriptPubKeyMan()
{
    SetupLegacyScriptPubKeyMan();
    return GetLegacyScriptPubKeyMan();
}
void CWallet::SetupLegacyScriptPubKeyMan()
{
    if (!m_internal_spk_managers.empty() || !m_external_spk_managers.empty() || !m_spk_managers.empty() || IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
        return;
    }
    auto spk_manager = std::unique_ptr<ScriptPubKeyMan>(new LegacyScriptPubKeyMan(*this));
    for (const auto& type : OUTPUT_TYPES) {
        m_internal_spk_managers[type] = spk_manager.get();
        m_external_spk_managers[type] = spk_manager.get();
    }
    m_spk_managers[spk_manager->GetID()] = std::move(spk_manager);
}
const CKeyingMaterial& CWallet::GetEncryptionKey() const