properly figure out correct thumbnail url for fanza

dlibrary/dlibrary.py

@@ -229,7 +229,16 @@ async def fetch_async(args):
                 authors = db_row.pop('authors')
                 tags = db_row.pop('tags')
                 if FANZA_ID_REGEX.fullmatch(work_id):
-                    thumbnail_url = f'https://doujin-assets.dmm.co.jp/digital/comic/{work_id}/{work_id}pl.jpg'
+                    candidate_urls = [
+                        f'https://doujin-assets.dmm.co.jp/digital/{work_type}/{work_id}/{work_id}pl.jpg'
+                        for work_type in ['comic', 'cg']
+                    ]
+                    thumbnail_url = None
+                    for url in candidate_urls:
+                        h = requests.head(url, allow_redirects=False)
+                        if h.status_code == 200:
+                            thumbnail_url = url
+                            break
                 elif FAKKU_ID_REGEX.fullmatch(work_id):
                     thumbnail_url = None
                 else: