Set Content-Length to 0, when returning an empty body

When returning 416 RangeNotSatisfiable in FileResultExecutorBase, set the Content-Length based on the length of the body instead of the length of the original file.
Bugfix for  :
https://github.com/aspnet/AspNetCore/issues/4943

src/Mvc/Mvc.Core/src/Infrastructure/FileResultExecutorBase.cs

@@ -322,6 +322,7 @@ namespace Microsoft.AspNetCore.Mvc.Infrastructure
                 // the current length of the selected resource.  e.g. */length
                 response.StatusCode = StatusCodes.Status416RangeNotSatisfiable;
                 httpResponseHeaders.ContentRange = new ContentRangeHeaderValue(fileLength);
+                response.ContentLength = 0;
 
                 return (range: null, rangeLength: 0, serveBody: false);
             }