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 IsMine(txout.scriptPubKey);
}
isminetype CWallet::IsMine(const CTxDestination& dest) const
{
    return IsMine(GetScriptForDestination(dest));
}
isminetype CWallet::IsMine(const CScript& script) const
{
    isminetype result = ISMINE_NO;
    for (const auto& spk_man_pair : m_spk_managers) {
        result = std::max(result, spk_man_pair.second->IsMine(script));
    }
    return result;
}
CAmount CWallet::GetCredit(const CTxOut& txout, const isminefilter& filter) const