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.
{
    AssertLockHeld(cs_wallet); 
    bool fCompressed = CanSupportFeature(FEATURE_COMPRPUBKEY); 
    CKey secret;
    
    int64_t nCreationTime = GetTime();
    CKeyMetadata metadata(nCreationTime);
    
    if (IsHDEnabled()) {
        DeriveNewChildKey(walletdb, metadata, secret, (CanSupportFeature(FEATURE_HD_SPLIT) ? internal : false));
    } else {
        secret.MakeNewKey(fCompressed);
    }
    
    if (fCompressed) {
        SetMinVersion(FEATURE_COMPRPUBKEY);
    }
    CPubKey pubkey = secret.GetPubKey();
    assert(secret.VerifyPubKey(pubkey));
    mapKeyMetadata[pubkey.GetID()] = metadata;
    UpdateTimeFirstKey(nCreationTime);
    if (!AddKeyPubKeyWithDB(walletdb, secret, pubkey)) {
        throw std::runtime_error(std::string(__func__) + ": AddKey failed");
    }
    return pubkey;
}
void CWallet::DeriveNewChildKey(CWalletDB &walletdb, CKeyMetadata& metadata, CKey& secret, bool internal)