Fix zero waypoints crash (#1978)

* return if the number of waypoints is zero.

* terminate the action.

* Succeed action instead of terminating.

nav2_waypoint_follower/src/waypoint_follower.cpp

@@ -127,6 +127,11 @@ WaypointFollower::followWaypoints()
     get_logger(), "Received follow waypoint request with %i waypoints.",
     static_cast<int>(goal->poses.size()));
 
+  if (goal->poses.size() == 0) {
+    action_server_->succeeded_current(result);
+    return;
+  }
+
   rclcpp::Rate r(loop_rate_);
   uint32_t goal_index = 0;
   bool new_goal = true;