[FIX] #452 Compressed item added to file cache -> error 500.

Author: rdeago

src/EmbedIO/Files/FileModule.cs

@@ -540,6 +540,7 @@ await source.CopyToAsync(compressor, WebServer.StreamCopyBufferSize, context.Can
                     }
 
                     content = memoryStream.ToArray();
+                    responseContentLength = content.Length;
                 }
 
                 cacheItem.SetContent(compressionMethod, content);