Fix -J when there are failed videos

yt_dlp/YoutubeDL.py

@@ -2908,6 +2908,8 @@ class YoutubeDL(object):
     @staticmethod
     def sanitize_info(info_dict, remove_private_keys=False):
         ''' Sanitize the infodict for converting to json '''
+        if info_dict is None:
+            return info_dict
         info_dict.setdefault('epoch', int(time.time()))
         remove_keys = {'__original_infodict'}  # Always remove this since this may contain a copy of the entire dict
         keep_keys = ['_type'],  # Always keep this to facilitate load-info-json