[youtube] Don't show warning for empty playlist description (Closes #54)

:ci skip dl

youtube_dlc/extractor/common.py

@@ -975,7 +975,7 @@ class InfoExtractor(object):
             video_info['id'] = playlist_id
         if playlist_title:
             video_info['title'] = playlist_title
-        if playlist_description:
+        if playlist_description is not None:
             video_info['description'] = playlist_description
         return video_info
 

youtube_dlc/extractor/youtube.py

@@ -2787,7 +2787,7 @@ class YoutubeTabIE(YoutubeBaseInfoExtractor):
                 data, lambda x: x['metadata']['playlistMetadataRenderer'], dict)
         if renderer:
             title = renderer.get('title')
-            description = renderer.get('description')
+            description = renderer.get('description', '')
             playlist_id = channel_id
             tags = renderer.get('keywords', '').split()
             thumbnails_list = (