Fix wrong ffmpeg map argument due to wrong calculation

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -2007,7 +2007,7 @@ namespace MediaBrowser.Controller.MediaEncoding
                 if (state.AudioStream.IsExternal)
                 {
                     int externalAudioMapIndex = state.SubtitleStream != null && state.SubtitleStream.IsExternal ? 2 : 1;
-                    int externalAudioStream = state.MediaSource.MediaStreams.FindIndex(i => i.Path == state.AudioStream.Path);
+                    int externalAudioStream = state.MediaSource.MediaStreams.Where(i => i.Path == state.AudioStream.Path).ToList().IndexOf(state.AudioStream);
 
                     args += string.Format(
                         CultureInfo.InvariantCulture,