Fix user admin bug and comment index bug

judge/views/comment.py

@@ -218,13 +218,18 @@ class CommentRevisionAjax(CommentMixin, DetailView):
     def get_context_data(self, **kwargs):
         context = super(CommentRevisionAjax, self).get_context_data(**kwargs)
         revisions = Version.objects.get_for_object(self.object).order_by("-revision")
+
+        if len(revisions) == 0:
+            raise Http404
+
         try:
             wanted = min(
                 max(int(self.request.GET.get("revision", 0)), 0), len(revisions) - 1
             )
-        except ValueError:
+            revision = revisions[wanted]
+        except (ValueError, IndexError):
             raise Http404
-        revision = revisions[wanted]
+
         data = json.loads(revision.serialized_data)
         try:
             context["body"] = data[0]["fields"]["body"]