Add more error handling for zmq_close/term

[mo3rfan]

• Add error handling everywhere for zmq_close and zmq_ctx_term
• Find out why the close and terms below errors out at some point in stress_test.py
  

  librtcdcpp/src/librtcdcpp.cpp

  Lines 184 to 189 in aaf774b

  	if (zmq_close (pusher) != 0) {
  	printf("\nZMQ close error: %s\n", strerror(errno));
  	}
  	if (zmq_ctx_term(child_to_parent_context) != 0) {
  	printf("\nZMQ term error: %s\n", strerror(errno));
  	}