Ignore badly formed ActivityPub object data (#406)

activities/models/post.py

@@ -737,9 +737,13 @@ class Post(StatorModel):
         Raises DoesNotExist if it's not found and create is False,
         or it's from a blocked domain.
         """
+        try:
             # Ensure the domain of the object's actor and ID match to prevent injection
             if urlparse(data["id"]).hostname != urlparse(data["attributedTo"]).hostname:
                 raise ValueError("Object's ID domain is different to its author")
+        except (TypeError, KeyError):
+            raise ValueError("Object data is not a recognizable ActivityPub object")
+
         # Do we have one with the right ID?
         created = False
         try: