Since glib 2.34, the thumbnails are in .cache/thumbnails, not in .thumbnails.
+#if GLIB_CHECK_VERSION (2, 34, 0)
+#define THUMB_FOLDER_GLOBAL ".cache/thumbnails"
+#else
#define THUMB_FOLDER_GLOBAL ".thumbnails"
#define THUMB_FOLDER_GLOBAL ".thumbnails"
#define THUMB_FOLDER_LOCAL ".thumblocal"
#define THUMB_FOLDER_NORMAL "normal"
#define THUMB_FOLDER_LARGE "large"
#define THUMB_FOLDER_LOCAL ".thumblocal"
#define THUMB_FOLDER_NORMAL "normal"
#define THUMB_FOLDER_LARGE "large"