Fix non utf-8 sse pending

[leehack]

Fix #43

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 45.98%. Comparing base (1f08bd5) to head (25a5d08).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/server/streamable_https.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
+ Coverage   45.55%   45.98%   +0.43%     
==========================================
  Files          15       16       +1     
  Lines        2880     2903      +23     
==========================================
+ Hits         1312     1335      +23     
  Misses       1568     1568              

Flag	Coverage Δ
unittests	45.98% <0.00%> (+0.43%)	⬆️

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