[luscious] fix IndexError for files without thumbnail (#5122)

gallery_dl/extractor/luscious.py

@@ -63,7 +63,11 @@ class LusciousAlbumExtractor(LusciousExtractor):
             image["num"] = num
             image["album"] = album
 
-            image["thumbnail"] = image.pop("thumbnails")[0]["url"]
+            try:
+                image["thumbnail"] = image.pop("thumbnails")[0]["url"]
+            except LookupError:
+                image["thumbnail"] = ""
+
             image["tags"] = [item["text"] for item in image["tags"]]
             image["date"] = text.parse_timestamp(image["created"])
             image["id"] = text.parse_int(image["id"])