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).
{
    LOCK(cs_wallet);
    m_wallet_flags |= flags;
    if (!WalletBatch(*database).WriteWalletFlags(m_wallet_flags))
        throw std::runtime_error(std::string(__func__) + ": writing wallet flags failed");
}
void CWallet::UnsetWalletFlag(uint64_t flag)
{
    WalletBatch batch(*database);
    UnsetWalletFlagWithDB(batch, flag);
}
void CWallet::UnsetWalletFlagWithDB(WalletBatch& batch, uint64_t flag)
{
    LOCK(cs_wallet);
    m_wallet_flags &= ~flag;
    if (!batch.WriteWalletFlags(m_wallet_flags))
        throw std::runtime_error(std::string(__func__) + ": writing wallet flags failed");
}
void CWallet::UnsetBlankWalletFlag(WalletBatch& batch)