fix: the correct handling is done in the iterator

* the thinking of handling negative revision numbers in this line with
  the list was wrong

invenio_records/api.py

@@ -544,7 +544,7 @@ def revert(self, revision_id):
         if self.model is None:
             raise MissingModelError()
 
-        revision = list(self.revisions)[revision_id]
+        revision = self.revisions[revision_id]
 
         with db.session.begin_nested():
             if self.send_signals: