fix: allow empty link_data

on different url that youtube

Author: 1ukastesar

cogs/streamlinks/cog.py

@@ -135,6 +135,9 @@ async def streamlinks_add(
             user = await self.get_user_string(user)
 
         link_data = self.get_link_data(link)
+        if not link_data:
+            link_data = {"image": None, "upload_date": None}
+
         if date is not None:
             link_data["upload_date"] = datetime.strptime(date, "%d.%m.%Y")
         else: