fix streaming trailers over HLS

MediaBrowser.Api/Playback/Hls/VideoHlsService.cs

@@ -206,6 +206,8 @@ namespace MediaBrowser.Api.Playback.Hls
             var framerate = state.VideoRequest.Framerate ?? 0;
 
             // We have to supply a framerate for hls, so if it's null, account for that here
+            if (state.VideoStream != null)
+            {
                 if (framerate.Equals(0))
                 {
                     framerate = state.VideoStream.AverageFrameRate ?? 0;
@@ -214,6 +216,7 @@ namespace MediaBrowser.Api.Playback.Hls
                 {
                     framerate = state.VideoStream.RealFrameRate ?? 0;
                 }
+            }
             if (framerate.Equals(0))
             {
                 framerate = 23.976;