mosquitto_pub: exit if server becomes unreachable and QOS > 0

Fixes eclipse/mosquitto#1899

In stdin line mode, mosquitto_pub will continue running and accepting
input even if/when/after publishing fails.  This condition is reached
when it first successfully establishes a connection and the server later
is unreachable.

Exiting with a non-zero exit code allows for much easier health
monitoring when used in a long-running pipe.

Signed-off-by: Dan White <dan.white@valpo.edu>

client/pub_client.c

@@ -256,8 +256,8 @@ int pub_stdin_line_loop(struct mosquitto *mosq)
 					rc = my_publish(mosq, &mid_sent, cfg.topic, buf_len_actual-1, line_buf, cfg.qos, cfg.retain);
 					pos = 0;
 					if(rc){
-						err_printf(&cfg, "Error: Publish returned %d, disconnecting.\n", rc);
-						mosquitto_disconnect_v5(mosq, MQTT_RC_DISCONNECT_WITH_WILL_MSG, cfg.disconnect_props);
+						err_printf(&cfg, "Error: Publish returned %d.\n", rc);
+						if(cfg.qos>0) return rc;
 					}
 					break;
 				}else{
@@ -275,8 +275,8 @@ int pub_stdin_line_loop(struct mosquitto *mosq)
 			if(pos != 0){
 				rc = my_publish(mosq, &mid_sent, cfg.topic, buf_len_actual, line_buf, cfg.qos, cfg.retain);
 				if(rc){
-					err_printf(&cfg, "Error: Publish returned %d, disconnecting.\n", rc);
-					mosquitto_disconnect_v5(mosq, MQTT_RC_DISCONNECT_WITH_WILL_MSG, cfg.disconnect_props);
+					err_printf(&cfg, "Error: Publish returned %d.\n", rc);
+					if(cfg.qos>0) return rc;
 				}
 			}
 			if(feof(stdin)){