Only set url on attachment select if attachment found

[tvdeyen]

What is this pull request for?

If we set the URL select2 will try to set the value but cannot find it but will hide the placeholder.

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.94%. Comparing base (c423ef0) to head (b477c1a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2882   +/-   ##
=======================================
  Coverage   95.94%   95.94%           
=======================================
  Files         230      230           
  Lines        6260     6260           
=======================================
  Hits         6006     6006           
  Misses        254      254           

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