[extractor] Do not exit early for unsuitable url_result

yt_dlp/extractor/common.py

@@ -3513,7 +3513,7 @@ class InfoExtractor:
     @classmethod
     def is_single_video(cls, url):
         """Returns whether the URL is of a single video, None if unknown"""
-        assert cls.suitable(url), 'The URL must be suitable for the extractor'
+        if cls.suitable(url):
             return {'video': True, 'playlist': False}.get(cls._RETURN_TYPE)
 
     @classmethod