fix DTS extraction of QSV HEVC streams (https://github.com/bluenviron/mediamtx/issues/3285)

[aler9]

Fixes bluenviron/mediamtx#3285

[codecov]

Codecov Report

Attention: Patch coverage is 97.64706% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 84.56%. Comparing base (b4e31e8) to head (b961b49).

Files	Patch %	Lines
pkg/codecs/h265/dts_extractor.go	77.77%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   84.55%   84.56%           
=======================================
  Files          72       72           
  Lines        5667     5734   +67     
=======================================
+ Hits         4792     4849   +57     
- Misses        648      653    +5     
- Partials      227      232    +5     

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