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.
int64_t m_max_keypool_index;
    std::map<CKeyID, int64_t> m_pool_key_to_index;
    int64_t nTimeFirstKey;
    /**
     * Private version of AddWatchOnly method which does not accept a
     * timestamp, and which will reset the wallet's nTimeFirstKey value to 1 if
     * the watch key did not previously have a timestamp associated with it.
     * Because this is an inherited virtual method, it is accessible despite
     * being marked private, but it is marked private anyway to encourage use
     * of the other AddWatchOnly which accepts a timestamp and sets
     * nTimeFirstKey more intelligently for more efficient rescans.
     */
    bool AddWatchOnly(const CScript& dest) override;
    std::unique_ptr<CWalletDBWrapper> dbw;
public:
    /*
     * Main wallet lock.
     * This lock protects all the fields added by CWallet.
     */
    mutable CCriticalSection cs_wallet;
    /** Get database handle used by this wallet. Ideally this function would
     * not be necessary.
     */
    CWalletDBWrapper& GetDBHandle()
    {
        return *dbw;
    }
    /** Get a name for this wallet for logging/debugging purposes.
     */
    std::string GetName() const