changed message depth of scan filter sub to 1 (#150)

* Check if parameters exist already before declaring them

* fixed coding style

* changed message depth of scan filter sub to 1

src/slam_toolbox_common.cpp

@@ -211,7 +211,7 @@ void SlamToolbox::setROSInterfaces()
     shared_from_this().get(), scan_topic_, rmw_qos_profile_sensor_data);
   scan_filter_ =
     std::make_unique<tf2_ros::MessageFilter<sensor_msgs::msg::LaserScan> >(
-    *scan_filter_sub_, *tf_, odom_frame_, 10, shared_from_this());
+    *scan_filter_sub_, *tf_, odom_frame_, 1, shared_from_this());
   scan_filter_->registerCallback(
     std::bind(&SlamToolbox::laserCallback, this, std::placeholders::_1));
 }