Raise error on 404 return code

[Gregy]

Hello, mt-files-downloader hapilly downloads error pages instead of content. For example if server returns 404 . I think error should be raised instead.

[leeroybrun]

Yes, you are right, thanks for the suggestion.

I will try to include this when updating to the latest version of mt-downloader ( #5 )

[Gregy]

Thank you :)