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).
{
    auto it = mapWallet.find(wtxid);
    assert(it != mapWallet.end());
    CWalletTx& thisTx = it->second;
    if (thisTx.IsCoinBase()) 
        return;
    for (const CTxIn& txin : thisTx.tx->vin)
        AddToSpends(txin.prevout, wtxid);
}
bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
{
    if (IsCrypted())
        return false;
    CKeyingMaterial _vMasterKey;
    _vMasterKey.resize(WALLET_CRYPTO_KEY_SIZE);
    GetStrongRandBytes(&_vMasterKey[0], WALLET_CRYPTO_KEY_SIZE);
    CMasterKey kMasterKey;
    kMasterKey.vchSalt.resize(WALLET_CRYPTO_SALT_SIZE);
    GetStrongRandBytes(&kMasterKey.vchSalt[0], WALLET_CRYPTO_SALT_SIZE);
    CCrypter crypter;
    int64_t nStartTime = GetTimeMillis();
    crypter.SetKeyFromPassphrase(strWalletPassphrase, kMasterKey.vchSalt, 25000, kMasterKey.nDerivationMethod);
    kMasterKey.nDeriveIterations = static_cast<unsigned int>(2500000 / ((double)(GetTimeMillis() - nStartTime)));
    nStartTime = GetTimeMillis();
    crypter.SetKeyFromPassphrase(strWalletPassphrase, kMasterKey.vchSalt, kMasterKey.nDeriveIterations, kMasterKey.nDerivationMethod);
    kMasterKey.nDeriveIterations = (kMasterKey.nDeriveIterations + static_cast<unsigned int>(kMasterKey.nDeriveIterations * 100 / ((double)(GetTimeMillis() - nStartTime)))) / 2;
    if (kMasterKey.nDeriveIterations < 25000)
        kMasterKey.nDeriveIterations = 25000;