[YoutubeDL] Fix format resolution when height is missing

youtube_dl/YoutubeDL.py

@@ -1798,7 +1798,7 @@ class YoutubeDL(object):
             else:
                 res = '%sp' % format['height']
         elif format.get('width') is not None:
-            res = '?x%d' % format['width']
+            res = '%dx?' % format['width']
         else:
             res = default
         return res