When website reports error like 'file not found' Download Manager doesn't display it.

[michael-gracy]

Tried downloading a file via Chrome, end up with a 0 byte file. Try a different browser and I see that there was a 'file not found' error being reported to the browser. Either the message needs to be passed through to the browser unchanged or a dialog box should be presented so that the user knows something happened.
@c0de0ff