Avoid infinite loop if stdin is closed prematurely in local_echo_demo.cpp

Author: Bryan Concari

example/local_echo_demo.cpp

@@ -134,7 +134,7 @@ int main() {
  // get std::string from user
  // send string data over network connection
  std::string s;
- while (s != "quit\n") {
+ while (s != "quit\n" && std::cin.good()) {
  std::cout << "> ";
  std::getline (std::cin, s);
  s += "\n"; // needed for deliminator