!clean command returns malformed API request
Since we added attachments to the deleted message logs the clean command was not updated to store this.

When running a clean command the following error is returned:
```
web_1       | Bad Request: /bot/deleted-messages
web_1       | "POST /bot/deleted-messages HTTP/1.1" 400 792
bot_1       | 2020-02-25 19:32:41,081 | bot.cogs.error_handler | DEBUG | API responded with 400 for command clean all: {'deletedmessage_set': [{'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}, {'attachments': ['This field may not be null.']}]}.
```

This is not critical since the clean command still operates, it just does not store deleted messages like intended.
diff --git a/bot/cogs/moderation/modlog.py b/bot/cogs/moderation/modlog.py
index 59ae6b58..81d95298 100644
--- a/bot/cogs/moderation/modlog.py
+++ b/bot/cogs/moderation/modlog.py
@@ -67,7 +67,7 @@ class ModLog(Cog, name="ModLog"):
                         'embeds': [embed.to_dict() for embed in message.embeds],
                         'attachments': attachment,
                     }
-                    for message, attachment in zip_longest(messages, attachments)
+                    for message, attachment in zip_longest(messages, attachments, fillvalue=[])
                 ]
             }
         )
['bot/cogs/moderation/modlog.py']