fix(static): send immediate empty responses for 304 handling

[markthree]

🔗 Linked issue

#1638

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

It just changes send(event, "") to return "" in 304。

It seems to be a problem with h3, if it returns undefined it will automatically jump to the next middleware

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #1639 (0e7e02d) into main (b1e676e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1639   +/-   ##
=======================================
  Coverage   77.76%   77.76%           
=======================================
  Files          76       76           
  Lines        7824     7824           
  Branches      803      803           
=======================================
  Hits         6084     6084           
  Misses       1738     1738           
  Partials        2        2           

[pi0]

Thanks!