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).
const uint256 CWalletTx::ABANDON_HASH(UINT256_ONE());
/** @defgroup mapWallet
 *
 * @{
 */
std::string COutput::ToString() const
{
    return strprintf("COutput(%s, %d, %d) [%s]", tx->GetHash().ToString(), i, nDepth, FormatMoney(tx->tx->vout[i].nValue));
}
const CWalletTx* CWallet::GetWalletTx(const uint256& hash) const
{
    LOCK(cs_wallet);
    std::map<uint256, CWalletTx>::const_iterator it = mapWallet.find(hash);
    if (it == mapWallet.end())
        return nullptr;
    return &(it->second);
}
void CWallet::UpgradeKeyMetadata()
{
    if (IsLocked() || IsWalletFlagSet(WALLET_FLAG_KEY_ORIGIN_METADATA)) {
        return;
    }
    auto spk_man = GetLegacyScriptPubKeyMan();
    if (!spk_man) {
        return;
    }
    spk_man->UpgradeKeyMetadata();
    SetWalletFlag(WALLET_FLAG_KEY_ORIGIN_METADATA);
}
bool CWallet::Unlock(const SecureString& strWalletPassphrase, bool accept_no_keys)