fix(crosswalk): fix calclation distance from the null polygons

[yuki-takagi-66]

Description

fix not to calculate the distance from the null polygon

Tests performed

psim and tier4 internal tests

Effects on system behavior

Not applicable.

Interface changes

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 15.48%. Comparing base (fe30833) to head (10f8990).
Report is 8 commits behind head on main.

❗ Current head 10f8990 differs from pull request most recent head ce9ad84

Please upload reports for the commit ce9ad84 to get more accurate results.

Files	Patch %	Lines
..._velocity_crosswalk_module/src/scene_crosswalk.hpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7122   +/-   ##
=======================================
  Coverage   15.48%   15.48%           
=======================================
  Files        1971     1971           
  Lines      136618   136618           
  Branches    44130    44131    +1     
=======================================
  Hits        21154    21154           
  Misses      92252    92252           
  Partials    23212    23212           

Flag	Coverage Δ		*Carryforward flag
differential	11.53% <0.00%> (?)
total	15.48% <ø> (+<0.01%)	⬆️	Carriedforward from fe30833

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

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