improve cookie handling during logins

gallery_dl/extractor/seiga.py

@@ -51,14 +51,14 @@ class SeigaExtractor(Extractor):
         """Login and set necessary cookies"""
         if not self._check_cookies(("user_session",)):
             username, password = self._get_auth_info()
-            self.session.cookies = self._login_impl(username, password)
+            self._update_cookies(self._login_impl(username, password))
 
     @cache(maxage=7*24*60*60, keyarg=1)
     def _login_impl(self, username, password):
-        """Actual login implementation"""
         self.log.info("Logging in as %s", username)
         url = "https://account.nicovideo.jp/api/v1/login"
         data = {"mail_tel": username, "password": password}
+
         self.request(url, method="POST", data=data)
         if "user_session" not in self.session.cookies:
             raise exception.AuthenticationError()