[instagram] support '/share/SHORTCODE' URLs (#8340)

i.e. "bare" /share/ links

gallery_dl/extractor/instagram.py

@@ -436,7 +436,8 @@ class InstagramExtractor(Extractor):
         return cursor
 
     def _update_cursor(self, cursor):
-        self.log.debug("Cursor: %s", cursor)
+        if cursor:
+            self.log.debug("Cursor: %s", cursor)
         self._cursor = cursor
         return cursor
 
@@ -461,16 +462,18 @@ class InstagramPostExtractor(InstagramExtractor):
     """Extractor for an Instagram post"""
     subcategory = "post"
     pattern = (r"(?:https?://)?(?:www\.)?instagram\.com"
-               r"/(?:share/()|[^/?#]+/)?(?:p|tv|reels?())/([^/?#]+)")
+               r"/(?:share()(?:/(?:p|tv|reels?()))?"
+               r"|(?:[^/?#]+/)?(?:p|tv|reels?()))"
+               r"/([^/?#]+)")
     example = "https://www.instagram.com/p/abcdefg/"
 
     def __init__(self, match):
-        if match[2] is not None:
+        if match[2] is not None or match[3] is not None:
             self.subcategory = "reel"
         InstagramExtractor.__init__(self, match)
 
     def posts(self):
-        share, reel, shortcode = self.groups
+        share, _, _, shortcode = self.groups
         if share is not None:
             url = text.ensure_http_scheme(self.url)
             headers = {