Prevent a possible segmentation fault (#4141) (#4147)

* Prevent a possible segmentation fault

#4141
Signed-off-by: Joni Pöllänen <[email protected]>

* Cleanup

Signed-off-by: Joni Pöllänen <[email protected]>

---------

Signed-off-by: Joni Pöllänen <[email protected]>

nav2_smac_planner/src/analytic_expansion.cpp

@@ -179,16 +179,17 @@ typename AnalyticExpansion<NodeT>::AnalyticExpansionNodes AnalyticExpansion<Node
 
   float d = state_space->distance(from(), to());
 
+  // A move of sqrt(2) is guaranteed to be in a new cell
+  static const float sqrt_2 = std::sqrt(2.0f);
+
   // If the length is too far, exit. This prevents unsafe shortcutting of paths
   // into higher cost areas far out from the goal itself, let search to the work of getting
   // close before the analytic expansion brings it home. This should never be smaller than
   // 4-5x the minimum turning radius being used, or planning times will begin to spike.
-  if (d > _search_info.analytic_expansion_max_length) {
+  if (d > _search_info.analytic_expansion_max_length || d < sqrt_2) {
     return AnalyticExpansionNodes();
   }
 
-  // A move of sqrt(2) is guaranteed to be in a new cell
-  static const float sqrt_2 = std::sqrt(2.0f);
   unsigned int num_intervals = static_cast<unsigned int>(std::floor(d / sqrt_2));
 
   AnalyticExpansionNodes possible_nodes;
@@ -248,7 +249,8 @@ typename AnalyticExpansion<NodeT>::AnalyticExpansionNodes AnalyticExpansion<Node
   if (!failure) {
     // We found 'a' valid expansion. Now to tell if its a quality option...
     const float max_cost = _search_info.analytic_expansion_max_cost;
-    if (*std::max_element(node_costs.begin(), node_costs.end()) > max_cost) {
+    auto max_cost_it = std::max_element(node_costs.begin(), node_costs.end());
+    if (max_cost_it != node_costs.end() && *max_cost_it > max_cost) {
       // If any element is above the comfortable cost limit, check edge cases:
       // (1) Check if goal is in greater than max_cost space requiring
       //  entering it, but only entering it on final approach, not in-and-out