[vk] Improve login

youtube_dl/extractor/vk.py

@@ -53,6 +53,7 @@ class VKBaseIE(InfoExtractor):
         # We will workaround this VK issue by resetting the remixlhk cookie to
         # the first one manually.
         cookies = url_handle.headers.get('Set-Cookie')
+        if cookies:
             if sys.version_info[0] >= 3:
                 cookies = cookies.encode('iso-8859-1')
             cookies = cookies.decode('utf-8')