[orca-list] Orca only reads the description of the first image

[Alex ARNAUD <alexarnaud hypra fr>]

Hello,

Enviromnent:
- Debian 9 "Stretch"
- Firefox xbx
- Orca master

Steps to reproduce:
1) Open this page https://github.com/mate-desktop/caja/pull/1249
2) Move the cursor on "3 participants"
3) Press down arrow

Result:
Orca announces the description of the first image

Expected result:
Orca should announce the description all the images

Note: If I tab on the image I obtain the description

Best regars,
Alex.