BUG: asset with invalid Operations Record results in error

[aqw]

An error results when running onyo edit on an asset that has an invalid Inventory Operations record in its history. onyo set does not error.

Invalid Inventory Operations records are "bad", but we cannot/should-not explode. Onyo needs to handle it gracefully and skip over the record. It should not be necessary to rewrite the entire repos history to heal it.

Also, this underlines the needs for an fsck check of Inventory Operations records. #599