[net] Remove assert(nMaxInbound > 0)

nMaxInbound might very well be 0 or -1, if the user prefers to keep
a small number of maxconnections.

Note: nMaxInbound of -1 means that the user set maxconnections
to 8 or less, but we still want to keep an additional slot for
the feeler connection.

Github-Pull: bitcoin#9008
Rebased-From: fa1c3c2

src/net.cpp

@@ -1021,7 +1021,6 @@ static void AcceptConnection(const ListenSocket& hListenSocket) {
     CAddress addr;
     int nInbound = 0;
     int nMaxInbound = nMaxConnections - (MAX_OUTBOUND_CONNECTIONS + MAX_FEELER_CONNECTIONS);
-    assert(nMaxInbound > 0);
 
     if (hSocket != INVALID_SOCKET)
         if (!addr.SetSockAddr((const struct sockaddr*)&sockaddr))