Disable "current view" download option when it's equivalent to the whole image

[Saira-A]

• [x] feature request

Previously, the option to download the current view of the image was hidden in the download dialogue if the current view was the same as the whole image, so there weren't two options to download the same thing. This was lost when the download dialogue was refactored to use React, so it would be nice to add it back in.