Corrected reporting function logic to complete group message variable

[TheChymera]

Addressing issue raised here: #1165 (comment)

[codecov]

Codecov Report

Base: 88.27% // Head: 88.25% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (d2d6836) compared to base (0439caf).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1166      +/-   ##
==========================================
- Coverage   88.27%   88.25%   -0.03%     
==========================================
  Files          73       73              
  Lines        8817     8818       +1     
==========================================
- Hits         7783     7782       -1     
- Misses       1034     1036       +2     

Flag	Coverage Δ
unittests	88.25% <0.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
dandi/cli/cmd_validate.py	73.03% <0.00%> (-0.83%)	⬇️
dandi/support/threaded_walk.py	93.10% <0.00%> (-1.73%)	⬇️

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[yarikoptic]

@TheChymera as PR title would be changelog entry -- please expand it slightly to become self-descriptive. Otherwise not clear what logic was fixed and why/for what reason. And btw -- for our own sake, what it resulted in really fixed, e.g. can you show on example output in master version vs this PR fixed one?

[TheChymera]

@yarikoptic edited.