fix segfault when path is empty (ros-navigation#3484) (ros-navigation…

…#3485)

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Co-authored-by: Guillaume Doisy <guillaume@dexory.com>
(cherry picked from commit 26ac810)

Co-authored-by: Guillaume Doisy <doisyg@users.noreply.github.com>

nav2_mppi_controller/src/critics/path_follow_critic.cpp

@@ -34,15 +34,16 @@ void PathFollowCritic::initialize()
 
 void PathFollowCritic::score(CriticData & data)
 {
- if (!enabled_ ||
+ const size_t path_size = data.path.x.shape(0) - 1;
+
+ if (!enabled_ || path_size == 0 ||
  utils::withinPositionGoalTolerance(threshold_to_consider_, data.state.pose.pose, data.path))
  {
  return;
  }
 
  utils::setPathFurthestPointIfNotSet(data);
  utils::setPathCostsIfNotSet(data, costmap_ros_);
- const size_t path_size = data.path.x.shape(0) - 1;
 
  auto offseted_idx = std::min(
  *data.furthest_reached_path_point + offset_from_furthest_, path_size);