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).
{
    return HasEncryptionKeys();
}
bool CWallet::IsLocked() const
{
    if (!IsCrypted()) {
        return false;
    }
    LOCK(cs_wallet);
    return vMasterKey.empty();
}
bool CWallet::Lock()
{
    if (!IsCrypted())
        return false;
    {
        LOCK(cs_wallet);
        vMasterKey.clear();
    }
    NotifyStatusChanged(this);
    return true;
}
bool CWallet::Unlock(const CKeyingMaterial& vMasterKeyIn, bool accept_no_keys)