Add comments noting that comma separated codec list is not supported in pure audio transcoding for now

MediaBrowser.Model/Dlna/StreamBuilder.cs

@@ -208,6 +208,10 @@ namespace MediaBrowser.Model.Dlna
 
                 var longBitrate = Math.Min(transcodingBitrate, playlistItem.AudioBitrate ?? transcodingBitrate);
                 playlistItem.AudioBitrate = longBitrate > int.MaxValue ? int.MaxValue : Convert.ToInt32(longBitrate);
+
+                // Pure audio transcoding does not support comma separated list of transcoding codec at the moment.
+                // So just use the AudioCodec as is would be safe enough as the _transcoderSupport.CanEncodeToAudioCodec
+                // would fail so this profile will not even be picked up.
                 if (playlistItem.AudioCodecs.Count == 0 && !string.IsNullOrWhiteSpace(transcodingProfile.AudioCodec))
                 {
                     playlistItem.AudioCodecs = [transcodingProfile.AudioCodec];