fix(attachement): if champ attachement is already destroyed don’t crash

[tchak]

https://demarches-simplifiees.sentry.io/issues/6202124446

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.39%. Comparing base (0c14bba) to head (d03c14b).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
app/controllers/attachments_controller.rb	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11272      +/-   ##
==========================================
- Coverage   84.39%   84.39%   -0.01%     
==========================================
  Files        1202     1202              
  Lines       26431    26432       +1     
  Branches     4974     4974              
==========================================
  Hits        22307    22307              
- Misses       4124     4125       +1     

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