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).
if (fExisted || IsMine(tx) || IsFromMe(tx))
        {
            /* Check if any keys in the wallet keypool that were supposed to be unused
             * have appeared in a new transaction. If so, remove those keys from the keypool.
             * This can happen when restoring an old wallet backup that does not contain
             * the mostly recently created transactions from newer versions of the wallet.
             */
            
            for (const CTxOut& txout: tx.vout) {
                for (const auto& spk_man_pair : m_spk_managers) {
                    spk_man_pair.second->MarkUnusedAddresses(txout.scriptPubKey);
                }
            }
            CWalletTx wtx(this, ptx);
            
            
            wtx.m_confirm = confirm;
            return AddToWallet(wtx, false);
        }
    }
    return false;
}
bool CWallet::TransactionCanBeAbandoned(const uint256& hashTx) const
{
    auto locked_chain = chain().lock();
    LOCK(cs_wallet);
    const CWalletTx* wtx = GetWalletTx(hashTx);
    return wtx && !wtx->isAbandoned() && wtx->GetDepthInMainChain() == 0 && !wtx->InMempool();
}
void CWallet::MarkInputsDirty(const CTransactionRef& tx)