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 (IsImmatureCoinBase() && IsInMainChain()) {
        return GetCachableAmount(IMMATURE_CREDIT, ISMINE_WATCH_ONLY, !fUseCache);
    }
    return 0;
}
CAmount CWalletTx::GetChange() const
{
    if (fChangeCached)
        return nChangeCached;
    nChangeCached = pwallet->GetChange(*tx);
    fChangeCached = true;
    return nChangeCached;
}
bool CWalletTx::InMempool() const
{
    return fInMempool;
}
bool CWalletTx::IsTrusted() const
{
    std::set<uint256> trusted_parents;
    LOCK(pwallet->cs_wallet);
    return pwallet->IsTrusted(*this, trusted_parents);
}
bool CWallet::IsTrusted(const CWalletTx& wtx, std::set<uint256>& trusted_parents) const