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 COutPoint outpoint(hash, n);
    std::pair<TxSpends::const_iterator, TxSpends::const_iterator> range;
    range = mapTxSpends.equal_range(outpoint);
    for (TxSpends::const_iterator it = range.first; it != range.second; ++it)
    {
        const uint256& wtxid = it->second;
        std::map<uint256, CWalletTx>::const_iterator mit = mapWallet.find(wtxid);
        if (mit != mapWallet.end()) {
            int depth = mit->second.GetDepthInMainChain();
            if (depth > 0  || (depth == 0 && !mit->second.isAbandoned()))
                return true; 
        }
    }
    return false;
}
void CWallet::AddToSpends(const COutPoint& outpoint, const uint256& wtxid)
{
    mapTxSpends.insert(std::make_pair(outpoint, wtxid));
    setLockedCoins.erase(outpoint);
    std::pair<TxSpends::iterator, TxSpends::iterator> range;
    range = mapTxSpends.equal_range(outpoint);
    SyncMetaData(range);
}
void CWallet::AddToSpends(const uint256& wtxid)