[extractor/BiliIntl] Fix subtitle extraction

Closes #3123

Authored by: HobbyistDev

yt_dlp/extractor/bilibili.py

@@ -789,7 +789,8 @@ class BiliIntlBaseIE(InfoExtractor):
     def json2srt(self, json):
         data = '\n\n'.join(
             f'{i + 1}\n{srt_subtitles_timecode(line["from"])} --> {srt_subtitles_timecode(line["to"])}\n{line["content"]}'
-            for i, line in enumerate(json['body']) if line.get('content'))
+            for i, line in enumerate(traverse_obj(json, (
+                'body', lambda _, l: l['content'] and l['from'] and l['to']))))
         return data
 
     def _get_subtitles(self, *, ep_id=None, aid=None):