"Download All as Zip" does not work when single file is selected

When a single file is selected the resulting zip is a picture file:

file sélection-1517566342844.zip 
sélection-1517566342844.zip: JPEG image data, JFIF standard 1.01, resolution (DPI), density 72x72, segment length 16, Exif Standard: [TIFF image data, big-endian, direntries=8, manufacturer=Canon, model=Canon EOS 450D, orientation=upper-left, xresolution=132, yresolution=140, resolutionunit=2, datetime=2011:04:26 22:54:32], baseline, precision 8, 2136x1424, frames 3

This can be reproduced on 9.10 and nightly:

1. Access https://nightly.nuxeo.com/nuxeo/ui/#!/browse/default-domain/workspaces/Sample%20Content
2. Check a picture
3. click "Download All as Zip" using the top-right button in the banner
4. observe a ZIP file is downloaded
5. try to extract it and it fails
6. rename de ZIP file with a JPG extension and it can be read as a picture.

So instead of bundling one file inside an archive it only renames it with a ZIP extension.