[weasyl:favorite] update

- use 'self.groups' to access userid and username
- safe one request by not doing an explicit username -> userid lookup
- safe one request by following the 'Next' link instead of detecting an
  empty page

gallery_dl/extractor/weasyl.py

@@ -160,50 +160,44 @@ class WeasylJournalsExtractor(WeasylExtractor):
 class WeasylFavoriteExtractor(WeasylExtractor):
     subcategory = "favorite"
     directory_fmt = ("{category}", "{user}", "Favorites")
-    pattern = BASE_PATTERN + r"favorites(?:\?userid=(\d+)|\/([\w~-]+))"
+    pattern = BASE_PATTERN + r"favorites(?:\?userid=(\d+)|/([^/?#]+))"
     example = "https://www.weasyl.com/favorites?userid=12345"
 
-    def __init__(self, match):
-        WeasylExtractor.__init__(self, match)
-        self.userid = match.group(1)
-        self.username = match.group(2)
-
     def items(self):
-        if self.userid is None and self.username is not None:
-            new_url = self.root + "/favorites/{}".format(self.username)
-            page = self.request(new_url).text
-            self.userid = text.extr(
-                page,
-                '<a class="more" href="/favorites?userid=',
-                '&amp'
-            )
-
+        userid, username = self.groups
         owner_login = lastid = None
-        url = self.root + "/favorites"
+
+        if username:
+            owner_login = username
+            path = "/favorites/" + username
+        else:
+            path = "/favorites"
         params = {
-            "userid" : self.userid,
+            "userid" : userid,
             "feature": "submit",
         }
 
         while True:
-            page = self.request(url, params=params).text
+            page = self.request(self.root + path, params=params).text
             pos = page.index('id="favorites-content"')
 
             if not owner_login:
                 owner_login = text.extr(page, '<a href="/~', '"')
 
-            new_posts = False
             for submitid in text.extract_iter(page, "/submissions/", "/", pos):
                 if submitid == lastid:
                     continue
-                new_posts = True
                 lastid = submitid
+
                 submission = self.request_submission(submitid)
                 if self.populate_submission(submission):
                     submission["user"] = owner_login
                     yield Message.Directory, submission
                     yield Message.Url, submission["url"], submission
 
-            if not new_posts:
+            try:
+                pos = page.index('">Next (', pos)
+            except ValueError:
                 return
-            params["nextid"] = submitid
+            path = text.unescape(text.rextract(page, 'href="', '"', pos)[0])
+            params = None