flickr download issue _d applied to mp4 files

[chrislewisdev2]

I had the same issue as #6360 and once the fix got committed, tried the nightly build and it worked great. I could then download JPEG files.

But I noticed when running on an album, it will not do the mp4 files as it fails when you add the _d to the filename. Some additional logic is needed to check the file type because mp4s worked fine in the previous version so I assume that doesn't need the extra _d.

If I get time to set this up, I'll do a PR.

Thank you for writing this utility - it is great.