Remove Content-Length header from DLNA HEAD request (#5335)

(cherry picked from commit d819a1d928)
Signed-off-by: Joshua M. Boniface <joshua@boniface.me>

Emby.Dlna/PlayTo/PlayToController.cs

@@ -132,7 +132,7 @@ namespace Emby.Dlna.PlayTo
 
         private async void OnDeviceMediaChanged(object sender, MediaChangedEventArgs e)
         {
-            if (_disposed)
+            if (_disposed || string.IsNullOrEmpty(e.OldMediaInfo.Url))
             {
                 return;
             }

Jellyfin.Api/Helpers/FileStreamResponseHelpers.cs

@@ -107,7 +107,8 @@ namespace Jellyfin.Api.Helpers
             // Headers only
             if (isHeadRequest)
             {
-                return new FileContentResult(Array.Empty<byte>(), contentType);
+                httpContext.Response.Headers[HeaderNames.ContentType] = contentType;
+                return new OkResult();
             }
 
             var transcodingLock = transcodingJobHelper.GetTranscodingLock(outputPath);