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.
mutable bool fDebitCached;
    mutable bool fCreditCached;
    mutable bool fImmatureCreditCached;
    mutable bool fAvailableCreditCached;
    mutable bool fWatchDebitCached;
    mutable bool fWatchCreditCached;
    mutable bool fImmatureWatchCreditCached;
    mutable bool fAvailableWatchCreditCached;
    mutable bool fChangeCached;
    mutable CAmount nDebitCached;
    mutable CAmount nCreditCached;
    mutable CAmount nImmatureCreditCached;
    mutable CAmount nAvailableCreditCached;
    mutable CAmount nWatchDebitCached;
    mutable CAmount nWatchCreditCached;
    mutable CAmount nImmatureWatchCreditCached;
    mutable CAmount nAvailableWatchCreditCached;
    mutable CAmount nChangeCached;
    CWalletTx()
    {
        Init(nullptr);
    }
    CWalletTx(const CWallet* pwalletIn, CTransactionRef arg) : CMerkleTx(std::move(arg))
    {
        Init(pwalletIn);
    }
    void Init(const CWallet* pwalletIn)
    {
        pwallet = pwalletIn;