gsheet_db bug fix on missing thumbnail

src/auto_archiver/databases/gsheet_db.py

@@ -71,8 +71,8 @@ class GsheetsDb(Database):
             batch_if_valid('screenshot', "\n".join(screenshot.urls))
 
         if (thumbnail := item.get_first_image("thumbnail")):
-            batch_if_valid('thumbnail', f'=IMAGE("{thumbnail.urls[0]}")')
-
+            if hasattr(thumbnail, "urls"):
+                batch_if_valid('thumbnail', f'=IMAGE("{thumbnail.urls[0]}")')
 
         if (browsertrix := item.get_media_by_id("browsertrix")):
             batch_if_valid('wacz', "\n".join(browsertrix.urls))