[youtube] Simplify automatic captions URL check (Closes #8287)

youtube_dl/extractor/youtube.py

@@ -964,8 +964,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         try:
             args = player_config['args']
             caption_url = args['ttsurl']
-            if caption_url is None or caption_url == "" or caption_url.isspace():
-                self._downloader.report_warning("No automatic captions")
+            if not caption_url:
+                self._downloader.report_warning(err_msg)
                 return {}
             timestamp = args['timestamp']
             # We get the available subtitles