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).
walletInstance->m_chain_notifications_handler = walletInstance->chain().handleNotifications(walletInstance);
    walletInstance->SetBroadcastTransactions(gArgs.GetBoolArg("-walletbroadcast", DEFAULT_WALLETBROADCAST));
    {
        walletInstance->WalletLogPrintf("setKeyPool.size() = %u\n",      walletInstance->GetKeyPoolSize());
        walletInstance->WalletLogPrintf("mapWallet.size() = %u\n",       walletInstance->mapWallet.size());
        walletInstance->WalletLogPrintf("mapAddressBook.size() = %u\n",  walletInstance->mapAddressBook.size());
    }
    return walletInstance;
}
void CWallet::postInitProcess()
{
    auto locked_chain = chain().lock();
    LOCK(cs_wallet);
    
    
    ReacceptWalletTransactions();
    
    chain().requestMempoolTransactions(*this);
}
bool CWallet::BackupWallet(const std::string& strDest) const
{
    return database->Backup(strDest);
}
CKeyPool::CKeyPool()
{
    nTime = GetTime();
    fInternal = false;
    m_pre_split = false;
}
CKeyPool::CKeyPool(const CPubKey& vchPubKeyIn, bool internalIn)