Opening two of the same wallet (tested in v0.18.0 of bitcoin-qt 64 bit) will cause a database collision, and will crash the program.

`[marshall@likon] {21:21} [~] $ bitcoin-0.18.0/bin/bitcoin-qt `
`terminate called after throwing an instance of 'std::runtime_error'  what():  BerkeleyBatch: Can't open database 8204388-wallet.dat (duplicates fileid 8b1c090000000800e25686350000000000000000 from 1352491-wallet.dat)`
`Aborted (core dumped)`

I have been able to reproduce the issue by importing two of the same wallet (with different filenames).
{
    UnsetWalletFlagWithDB(batch, WALLET_FLAG_BLANK_WALLET);
}
bool CWallet::IsWalletFlagSet(uint64_t flag) const
{
    return (m_wallet_flags & flag);
}
bool CWallet::SetWalletFlags(uint64_t overwriteFlags, bool memonly)
{
    LOCK(cs_wallet);
    m_wallet_flags = overwriteFlags;
    if (((overwriteFlags & KNOWN_WALLET_FLAGS) >> 32) ^ (overwriteFlags >> 32)) {
        
        return false;
    }
    if (!memonly && !WalletBatch(*database).WriteWalletFlags(m_wallet_flags)) {
        throw std::runtime_error(std::string(__func__) + ": writing wallet flags failed");
    }
    return true;
}
int64_t CWalletTx::GetTxTime() const
{
    int64_t n = nTimeSmart;
    return n ? n : nTimeReceived;
}
bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout, bool use_max_sig) const