Called when a client is entering the game.
Whether a client has a steamid is undefined until OnClientAuthorized is called, which may occur either before or after OnClientPutInServer. Similarly, use OnClientPostAdminCheck() if you need to verify whether connecting players are admins.
GetClientCount() will include clients as they are passed through this function, as clients are already in game at this point.
void OnClientPutInServer(int client)