With slideshow desktop wallpaper plugin, selecting "Open wallpaper Image" from RMB does nothing.
https://bugs.kde.org/show_bug.cgi?id=394035
I'm not really sure this is the right place to commit, but the code looks identical to /usr/share/plasma/wallpapers/org.kde.slideshow/contents/ui/main.qml on my KDE 5.12.80 installation, so I'm assuming its related.