wallpaper filechooser has no preview

[Denis Jacquerye]

the Add Wallpaper filechooser window that I have when I go in the
Desktop Background Preferences doesn't show any preview of the picture
I might want to add to the list of available wallpapers. I don't know
if that's an upstream bug/feature, but it's rather annoying, at least
I find.
If I want to add one picture from a directory containing many, and I
don't remember it's name, I have to add one, see if it's the one I
wanted, if not I have to remove it from the list of wallpapers and
keep looking that way.

It would make more sense to simply have a preview in the Add Wallpaper
filechooser.

Denis