Built against `master` branch 801dd40666d1e6009920ad3ff755c7bb993b2a62:

If I have no wallet.dat file and run:

    bitcoind -usehd=0

A new wallet.dat file is created and an HD seed is assigned.

I see an error message in the source:

    "Error loading %s: You can't disable HD on an already existing HD wallet or create new non-HD wallets."

but that doesn't get shown because `fFirstRun` is true, and so the code which checks for `-usehd` values doesn't run.

If it's no longer possible to create non-HD wallets, specifying -usehd=0 when creating a wallet should be an error, and not get silently ignored.
{
    if (pwallet == nullptr)
        return 0;
    
    if (IsCoinBase() && GetBlocksToMaturity() > 0)
        return 0;
    if (fUseCache && fAvailableCreditCached)
        return nAvailableCreditCached;
    CAmount nCredit = 0;
    uint256 hashTx = GetHash();
    for (unsigned int i = 0; i < tx->vout.size(); i++)
    {
        if (!pwallet->IsSpent(hashTx, i))
        {
            const CTxOut &txout = tx->vout[i];
            nCredit += pwallet->GetCredit(txout, ISMINE_SPENDABLE);
            if (!MoneyRange(nCredit))
                throw std::runtime_error(std::string(__func__) + " : value out of range");
        }
    }
    nAvailableCreditCached = nCredit;
    fAvailableCreditCached = true;
    return nCredit;
}
CAmount CWalletTx::GetImmatureWatchOnlyCredit(const bool& fUseCache) const