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_wallets);
    auto it = g_load_wallet_fns.emplace(g_load_wallet_fns.end(), std::move(load_wallet));
    return interfaces::MakeHandler([it] { LOCK(cs_wallets); g_load_wallet_fns.erase(it); });
}
static Mutex g_wallet_release_mutex;
static std::condition_variable g_wallet_release_cv;
static std::set<std::string> g_unloading_wallet_set;
static void ReleaseWallet(CWallet* wallet)
{
    const std::string name = wallet->GetName();
    wallet->WalletLogPrintf("Releasing wallet\n");
    wallet->Flush();
    delete wallet;
    
    {
        LOCK(g_wallet_release_mutex);
        if (g_unloading_wallet_set.erase(name) == 0) {
            
            return;
        }
    }
    g_wallet_release_cv.notify_all();
}
void UnloadWallet(std::shared_ptr<CWallet>&& wallet)