fix issue with audio transcoding

MediaBrowser.Api/Playback/Hls/DynamicHlsService.cs

@@ -865,7 +865,7 @@ namespace MediaBrowser.Api.Playback.Hls
             {
                 framerate = Math.Round(state.TargetFramerate.GetValueOrDefault(), 3);
             }
-            else if (state.VideoStream.RealFrameRate.HasValue)
+            else if (state.VideoStream?.RealFrameRate != null)
             {
                 framerate = Math.Round(state.VideoStream.RealFrameRate.GetValueOrDefault(), 3);
             }