[vine] Make sure the title won't be empty

And fix a relevant TwitterCard test case

ChangeLog

@@ -1,6 +1,7 @@
 version <unreleased>
 
 Extractors
+* [vine] Make sure the title won't be empty
 + [twitter] Support HLS streams in vmap URLs
 + [periscope] Support pscp.tv URLs in embedded frames
 * [niconico] Fix authentication error handling (#12486)

youtube_dl/extractor/twitter.py

@@ -91,6 +91,7 @@ class TwitterCardIE(TwitterBaseIE):
                 'uploader_id': '1189339351084113920',
                 'uploader': 'ArsenalTerje',
                 'title': 'Vine by ArsenalTerje',
+                'timestamp': 1447451307,
             },
             'add_ie': ['Vine'],
         }, {

youtube_dl/extractor/vine.py

@@ -92,10 +92,12 @@ def video_url(kind):
 
         username = data.get('username')
 
+        alt_title = 'Vine by %s' % username if username else None
+
         return {
             'id': video_id,
-            'title': data.get('description'),
-            'alt_title': 'Vine by %s' % username if username else None,
+            'title': data.get('description') or alt_title or 'Vine video',
+            'alt_title': alt_title,
             'thumbnail': data.get('thumbnailUrl'),
             'timestamp': unified_timestamp(data.get('created')),
             'uploader': username,