mkv: fix statement has no effect warning

modules/demux/mkv/matroska_segment_parse.cpp

@@ -1098,10 +1098,9 @@ void matroska_segment_c::ParseTracks( KaxTracks *tracks )
 
     TrackHandlers::Dispatcher().iterate( tracks->begin(), tracks->end(), &payload );
 
-    auto t = matroska_segment_c::tracks.begin();
-    for (t; t != matroska_segment_c::tracks.end(); ++t)
+    for (auto &track : matroska_segment_c::tracks)
     {
-        pcr_shift = std::max(pcr_shift, t->second->i_codec_delay);
+        pcr_shift = std::max(pcr_shift, track.second->i_codec_delay);
     }
 }