No longer builds after recent gnome-desktop API changes
Recent gnome-desktop-3 and -4 add GCancellable and GError to the thumbnail API so:
src/main.c: In function 'copy_thumbnail_from_file':
src/main.c:360:42: error: too few arguments to function 'gnome_desktop_thumbnail_factory_generate_thumbnail'
360 | pixbuf = gnome_desktop_thumbnail_factory_generate_thumbnail (factory, file_uri, file_mime_type);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~