fix(planning_evaluator): fix crashes with empty trajectories

[maxime-clem]

Description

Crashes were caused by subtracting 1 from unsigned integer (size_t), causing crashes with empty trajectories (where the size = 0).

To reproduce the crash, you can publish an empty trajectory with the following command:

ros2 topic pub /planning/scenario_planning/trajectory autoware_auto_planning_msgs/msg/Trajectory "{header: {stamp: now, frame_id: "base_link"}}"

Tests performed

PSim

Effects on system behavior

Not applicable.

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[kyoichi-sugahara]

@maxime-clem
Thanks!
How did you detect this bug?

[kyoichi-sugahara]

LGTM!

[maxime-clem]

@maxime-clem Thanks! How did you detect this bug?

@TakaHoribe found this bug (#6126).
I added instructions on how to reproduce the crash in the PR description.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (19009f7) 14.61% compared to head (f112e4c) 14.61%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6129   +/-   ##
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  Coverage   14.61%   14.61%           
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  Files        1860     1860           
  Lines      127417   127417           
  Branches    37286    37286           
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+ Hits        18621    18622    +1     
  Misses      87884    87884           
+ Partials    20912    20911    -1     

Flag	Coverage Δ		*Carryforward flag
differential	58.69% <100.00%> (?)
total	14.61% <ø> (-0.01%)	⬇️	Carriedforward from 19009f7

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