fix(drivable_area_expansion): fix invalid access

[satoshi-ota]

Description

Related ticket: https://tier4.atlassian.net/browse/RT1-5459

Add guard to prevent std::out_of_range in following loop.

  // Insert middle points
  for (size_t i = start_idx + 1; i <= goal_idx; ++i) {
    const auto & next_point = tmp_bound.at(i);
    const double dist = tier4_autoware_utils::calcDistance2d(processed_bound.back(), next_point);
    if (dist > overlap_threshold) {
      processed_bound.push_back(next_point);
    }
  }

Tests performed

Psim

Effects on system behavior

Nothing.

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 14.73%. Comparing base (48d20f1) to head (068c531).
Report is 12 commits behind head on main.

Files	Patch %	Lines
...s/drivable_area_expansion/static_drivable_area.cpp	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6566      +/-   ##
==========================================
- Coverage   14.78%   14.73%   -0.06%     
==========================================
  Files        1917     1917              
  Lines      132038   133724    +1686     
  Branches    39228    40039     +811     
==========================================
+ Hits        19523    19705     +182     
- Misses      90725    92023    +1298     
- Partials    21790    21996     +206     

Flag	Coverage Δ		*Carryforward flag
differential	10.75% <0.00%> (?)
total	14.78% <ø> (ø)		Carriedforward from 48d20f1

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