fix(os/stream): dont set content length header if size is 0

[vnghia]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 80.21%. Comparing base (f729f4a) to head (bad6357).

Files	Patch %	Lines
src/open_subsonic/media_retrieval/stream.rs	95.83%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #234      +/-   ##
==========================================
- Coverage   80.22%   80.21%   -0.02%     
==========================================
  Files         213      213              
  Lines       11895    11901       +6     
  Branches    11895    11901       +6     
==========================================
+ Hits         9543     9546       +3     
- Misses       1707     1708       +1     
- Partials      645      647       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.