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.

{
    {
        LOCK(cs_setBanned);
        setBanned.clear();
        setBannedIsDirty = true;
    }
    DumpBanlist(); 
    if(clientInterface)
        clientInterface->BannedListChanged();
}
bool CConnman::IsBanned(CNetAddr ip)
{
    bool fResult = false;
    {
        LOCK(cs_setBanned);
        for (banmap_t::iterator it = setBanned.begin(); it != setBanned.end(); it++)
        {
            CSubNet subNet = (*it).first;
            CBanEntry banEntry = (*it).second;
            if(subNet.Match(ip) && GetTime() < banEntry.nBanUntil)
                fResult = true;
        }
    }
    return fResult;
}
bool CConnman::IsBanned(CSubNet subnet)