bsonObjToArray and bsonGetImmutable are sibling functions in the MozJS BSON binding layer. bsonGetImmutable ensures the BSONObj it works with is owned before creating JS wrappers around it;  bsonObjToArray does not apply the same treatment. This inconsistency can lead to incorrect behaviour when operating on sub-document wrappers. Bring bsonObjToArray in line with the established pattern used by bsonGetImmutable.