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).
wtx.m_confirm.nIndex = 0;
            wtx.m_confirm.hashBlock = hashBlock;
            wtx.m_confirm.block_height = conflicting_height;
            wtx.setConflicted();
            wtx.MarkDirty();
            batch.WriteTx(wtx);
            
            TxSpends::const_iterator iter = mapTxSpends.lower_bound(COutPoint(now, 0));
            while (iter != mapTxSpends.end() && iter->first.hash == now) {
                 if (!done.count(iter->second)) {
                     todo.insert(iter->second);
                 }
                 iter++;
            }
            
            
            MarkInputsDirty(wtx.tx);
        }
    }
}
void CWallet::SyncTransaction(const CTransactionRef& ptx, CWalletTx::Confirmation confirm, bool update_tx)
{
    if (!AddToWalletIfInvolvingMe(ptx, confirm, update_tx))
        return; 
    
    
    
    MarkInputsDirty(ptx);
}
void CWallet::transactionAddedToMempool(const CTransactionRef& ptx) {