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.
{
    CKey key;
    key.MakeNewKey(true);
    int64_t nCreationTime = GetTime();
    CKeyMetadata metadata(nCreationTime);
    
    CPubKey pubkey = key.GetPubKey();
    assert(key.VerifyPubKey(pubkey));
    
    metadata.hdKeypath     = "m";
    metadata.hdMasterKeyID = pubkey.GetID();
    {
        LOCK(cs_wallet);
        
        mapKeyMetadata[pubkey.GetID()] = metadata;
        
        if (!AddKeyPubKey(key, pubkey))
            throw std::runtime_error(std::string(__func__) + ": AddKeyPubKey failed");
    }
    return pubkey;
}
bool CWallet::SetHDMasterKey(const CPubKey& pubkey)