[extractor/youtube] Ignore incomplete data for comment threads by default (#7475)

For both `--ignore-errors` and `--ignore-errors only_download`. Pass `--no-ignore-errors` to not ignore.

Closes https://github.com/yt-dlp/yt-dlp/issues/7474

Authored by: coletdjnz

yt_dlp/extractor/youtube.py

@@ -3426,7 +3426,9 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                         # Pinned comments may appear a second time in newest first sort
                         # See: https://github.com/yt-dlp/yt-dlp/issues/6712
                         continue
-                    self.report_warning('Detected YouTube comments looping. Stopping comment extraction as we probably cannot get any more.')
+                    self.report_warning(
+                        'Detected YouTube comments looping. Stopping comment extraction '
+                        f'{"for this thread" if parent else ""} as we probably cannot get any more.')
                     yield
                 else:
                     tracker['seen_comment_ids'].add(comment['id'])
@@ -3517,11 +3519,17 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 # Ignore incomplete data error for replies if retries didn't work.
                 # This is to allow any other parent comments and comment threads to be downloaded.
                 # See: https://github.com/yt-dlp/yt-dlp/issues/4669
-                if 'incomplete data' in str(e).lower() and parent and self.get_param('ignoreerrors') is True:
+                if 'incomplete data' in str(e).lower() and parent:
+                    if self.get_param('ignoreerrors') in (True, 'only_download'):
                         self.report_warning(
                             'Received incomplete data for a comment reply thread and retrying did not help. '
-                        'Ignoring to let other comments be downloaded.')
+                            'Ignoring to let other comments be downloaded. Pass --no-ignore-errors to not ignore.')
+                        return
                     else:
+                        raise ExtractorError(
+                            'Incomplete data received for comment reply thread. '
+                            'Pass --ignore-errors to ignore and allow rest of comments to download.',
+                            expected=True)
                 raise
             is_forced_continuation = False
             continuation = None