mavlink: Only send the distance sensor message if the topic actually updates

src/modules/mavlink/mavlink_messages.cpp

@@ -1339,7 +1339,7 @@ protected:
 
 	void send(const hrt_abstime t)
 	{
-		(void)range_sub->update(t);
+		if (range_sub->update(t)) {
 
 			uint8_t type;
 
@@ -1356,6 +1356,7 @@ protected:
 			mavlink_msg_distance_sensor_send(_channel, range->timestamp / 1000, type, id, orientation,
 				range->minimum_distance*100, range->maximum_distance*100, range->distance*100, covariance);
 		}
+	}
 };
 
 MavlinkStream *streams_list[] = {