flatpak: Properly fallback to loading an app's info from...

flatpak: Properly fallback to loading an app's info from flatpak_installed_ref_load_appdata() when appstream is confused

AppStream doesn't support having 2 apps with the same id like it happens
on flathub for the separate beta/stable/lts branches.
This way we won't be showing the wrong version number when updating one
of these apps.