Add clarification comment for checking HLS audio-only tracks

Author: napoleon-na

packages/video_player/video_player_avfoundation/darwin/video_player_avfoundation/Sources/video_player_avfoundation/FVPVideoPlayer.m

@@ -383,6 +383,8 @@ - (void)setupEventSinkIfReadyToPlay {
     }
 
     BOOL hasVideoTracks = [asset tracksWithMediaType:AVMediaTypeVideo].count != 0;
+    // In HLS streams, AVAsset may not always provide track information because it is a streaming format.
+    // For audio-only HLS files, track information must be checked using `currentItem.tracks.count`.
     BOOL hasNoTracks = currentItem.tracks.count == 0 && asset.tracks.count == 0;
 
     // The player has not yet initialized when it has no size, unless it is an audio-only track.