[CON-153] fix: lightclient: divergence detector should return upon sending error

[arajasek]

If I'm understanding this code correctly, we should always return after adding an error to the channel. I think we're just missing two return statements.

Note: I wound up here investigating a flaky test failure, but I think this is an actual bug, not a test issue.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 23, 2025, 3:47 PM

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The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 18, 2025, 7:59 PM

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 41.99%. Comparing base (3078fb2) to head (539dc31).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sei-tendermint/light/detector.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2634      +/-   ##
==========================================
- Coverage   42.00%   41.99%   -0.02%     
==========================================
  Files        1018     1018              
  Lines       84807    84809       +2     
==========================================
- Hits        35626    35614      -12     
- Misses      45838    45851      +13     
- Partials     3343     3344       +1     

Flag	Coverage Δ
sei-cosmos	38.20% <ø> (-0.01%)	⬇️
sei-db	69.28% <ø> (+0.21%)	⬆️
sei-tendermint	47.29% <50.00%> (-0.04%)	⬇️

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Files with missing lines	Coverage Δ
sei-tendermint/light/detector.go	72.30% <50.00%> (-0.24%)	⬇️

... and 12 files with indirect coverage changes

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