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 (nIndex != -1) {
        m_spk_man->KeepDestination(nIndex, type);
    }
    nIndex = -1;
    address = CNoDestination();
}
void ReserveDestination::ReturnDestination()
{
    if (nIndex != -1) {
        m_spk_man->ReturnDestination(nIndex, fInternal, address);
    }
    nIndex = -1;
    address = CNoDestination();
}
void CWallet::LockCoin(const COutPoint& output)
{
    AssertLockHeld(cs_wallet);
    setLockedCoins.insert(output);
}
void CWallet::UnlockCoin(const COutPoint& output)