Update appstream-glib to 0.7.8

[bochecha]

New Features:

• Add as_store_get_app_by_launchable() (Richard Hughes)
• Add as_utils_unique_id_match() (Richard Hughes)
• Add as_version_string() for fwupd (Richard Hughes)
• Add support for component agreements (Richard Hughes)

Bugfixes:

• Correctly compare version numbers like '1.2.3' and '1.2.3a' (Richard Hughes)
• Don't include the path component in the name when parsing the package filename (Richard Hughes)
• If the launchable is specified don't guess it when composing (Richard Hughes)
• Never add more than one component to the AppStream store when composing (Richard Hughes)
• Veto apps that have empty OnlyShowIn= (Kalev Lember)

[bochecha]

I'm especially interested in these two changes:

• Correctly compare version numbers like '1.2.3' and '1.2.3a'

  I need this to use the correct versions in Blender in Flathub

• Never add more than one component to the AppStream store when composing

  This is problematic for apps using <id>foo.bar.Baz</id> in their appdata file, with a desktop file called foo.bar.Baz.desktop, which is going to be most apps in the future (as that's the recommended way to do it)

  That creates two <component> instead of one in the resulting appstream, and among other things it confuses clients (like GNOME Software), making them select/display the wrong screenshot by default. (I originally saw the problem with Dino, which I'm working on flatpaking)

Of course, the other bug fixes are good to take, I'm only speaking for what interests me here. 🙂