Filter the package list to only include the latest version
Only consider the RPM file if it loaded okay
Specify the file extension in the AppStream <icon> tag

The AppStream specification is very vague here. From a performance point of view,
you don't want to be stat()ing the 'icon', 'icon.png', 'icon.svg', 'icon.gif'
at software center startup time, so it does help to be specific in the metadata
to speed things up.