Current bitcoin-master on testnet, `maxconnections=8` in the config file. Running in VM that doesn't have public IP and is not reachable from the Internet.

Wait until you have 8 peers.

```
telnet localhost 18333
```

It will result in:

```
Assertion failed: (nMaxInbound > 0), function AcceptConnection, file net.cpp, line 973.
```

First found in https://github.com/bitcoin/bitcoin/pull/8996, but can be reproduced on master.

{
    DumpAddresses();
    DumpBanlist();
}
void CConnman::ProcessOneShot()
{
    std::string strDest;
    {
        LOCK(cs_vOneShots);
        if (vOneShots.empty())
            return;
        strDest = vOneShots.front();
        vOneShots.pop_front();
    }
    CAddress addr;
    CSemaphoreGrant grant(*semOutbound, true);
    if (grant) {
        if (!OpenNetworkConnection(addr, false, &grant, strDest.c_str(), true))
            AddOneShot(strDest);
    }
}
void CConnman::ThreadOpenConnections()
{
    
    if (mapArgs.count("-connect") && mapMultiArgs["-connect"].size() > 0)
    {
        for (int64_t nLoop = 0;; nLoop++)
        {
            ProcessOneShot();
            BOOST_FOREACH(const std::string& strAddr, mapMultiArgs["-connect"])