[instagram:user] Fix extraction (fixes #9059)

The URL for the next page was incorrect and we always got the same page, therefore it got trapped in an infinite loop.

youtube_dl/extractor/instagram.py

@@ -152,7 +152,7 @@ class InstagramUserIE(InfoExtractor):
 
             if not page['items']:
                 break
-            max_id = page['items'][-1]['id']
+            max_id = page['items'][-1]['id'].split('_')[0]
             media_url = (
                 'http://instagram.com/%s/media?max_id=%s' % (
                     uploader_id, max_id))