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 std::string name = wallet->GetName();
    {
        LOCK(g_wallet_release_mutex);
        auto it = g_unloading_wallet_set.insert(name);
        assert(it.second);
    }
    
    
    
    wallet->NotifyUnload();
    
    wallet.reset();
    {
        WAIT_LOCK(g_wallet_release_mutex, lock);
        while (g_unloading_wallet_set.count(name) == 1) {
            g_wallet_release_cv.wait(lock);
        }
    }
}
std::shared_ptr<CWallet> LoadWallet(interfaces::Chain& chain, const WalletLocation& location, std::string& error, std::vector<std::string>& warnings)