h265: fix DTS extractor regression after #245

[aler9]

IDR frames which are also B-frames are supported again.

[codecov]

Codecov Report

❌ Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.81%. Comparing base (e1eba3d) to head (dbeee4e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/codecs/h265/dts_extractor.go	76.47%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #247      +/-   ##
==========================================
- Coverage   83.87%   83.81%   -0.07%     
==========================================
  Files          87       87              
  Lines        7548     7561      +13     
==========================================
+ Hits         6331     6337       +6     
- Misses        913      917       +4     
- Partials      304      307       +3     

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