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.

{
    
    unsigned int nRemaining = 24 - nHdrPos;
    unsigned int nCopy = std::min(nRemaining, nBytes);
    memcpy(&hdrbuf[nHdrPos], pch, nCopy);
    nHdrPos += nCopy;
    
    if (nHdrPos < 24)
        return nCopy;
    
    try {
        hdrbuf >> hdr;
    }
    catch (const std::exception&) {
        return -1;
    }
    
    if (hdr.nMessageSize > MAX_SIZE)
            return -1;
    
    in_data = true;
    return nCopy;
}
int CNetMessage::readData(const char *pch, unsigned int nBytes)