[afreecatv] Fix adult (19+) VODs

AfreecaTV marks segments of VODs, or entire VODs, as adult content. When
accessing a VOD with adult segments from an underage account or when not
logged in, the first request fails with a "PARTIAL_ADULT" error flag,
and we retry with the partialView=SKIP_ADULT query parameter. This
allows us to download the segments of the video that are not marked as
adult.

Now, when accessing a VOD that is entirely marked as adult content,
the first request fails with an "ADULT" error flag, *even if logged in
to an adult account*. The web client presents a click-through warning,
and refetches the XML with adultView=ADULT_VIEW.

This commit adjusts the existing retry logic for PARTIAL_ADULT to also
support retrying ADULT VODs with the required parameter.

If the same ADULT error is returned on the second attempt, we raise the
same error as before. This will occur if we are not logged in to an
adult account.

At this time it does not appear that the click-through warning has been
added to PARTIAL_ADULT VODs, so if we are logged in, our first request
is still successful. Therefore, the PARTIAL_ADULT logic does not need
to be changed.

The VODs mentioned in the below tickets are both now private, so I
cannot test the given URLs, but I believe that this:

Fixes #26622, fixes #26926

youtube_dl/extractor/afreecatv.py

@@ -237,6 +237,7 @@ class AfreecaTVIE(InfoExtractor):
             r'nTitleNo\s*=\s*(\d+)', webpage, 'title', default=video_id)
 
         partial_view = False
+        adult_view = False
         for _ in range(2):
             query = {
                 'nTitleNo': video_id,
@@ -245,6 +246,8 @@ class AfreecaTVIE(InfoExtractor):
             }
             if partial_view:
                 query['partialView'] = 'SKIP_ADULT'
+            if adult_view:
+                query['adultView'] = 'ADULT_VIEW'
             video_xml = self._download_xml(
                 'http://afbbs.afreecatv.com:8080/api/video/get_video_info.php',
                 video_id, 'Downloading video info XML%s'
@@ -264,6 +267,9 @@ class AfreecaTVIE(InfoExtractor):
                 partial_view = True
                 continue
             elif flag == 'ADULT':
+                if not adult_view:
+                    adult_view = True
+                    continue
                 error = 'Only users older than 19 are able to watch this video. Provide account credentials to download this content.'
             else:
                 error = flag