fix(obstacle_stop): add vector size guard

[yuki-takagi-66]

Description

add vector size guard to fix this issue #6151

Tests performed

psim tests

Effects on system behavior

Not applicable.

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[brkay54]

LGTM!

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (82d1b10) 14.40% compared to head (b08e745) 14.40%.
Report is 9 commits behind head on main.

Files	Patch %	Lines
planning/obstacle_stop_planner/src/node.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6254      +/-   ##
==========================================
- Coverage   14.40%   14.40%   -0.01%     
==========================================
  Files        1906     1906              
  Lines      129850   129851       +1     
  Branches    37571    37572       +1     
==========================================
  Hits        18700    18700              
- Misses      90157    90158       +1     
  Partials    20993    20993              

Flag	Coverage Δ		*Carryforward flag
differential	8.84% <0.00%> (?)
total	14.40% <ø> (ø)		Carriedforward from 82d1b10

*This pull request uses carry forward flags. Click here to find out more.

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