color: make invalid id illegal
This started from !90 (closed) where it was desireable for a compositor to send invalid image description ids because it does not track and de-duplicate image description records.
Concensus decided the opposite: the id number must be valid. The ability to skip get_information request was seen valuable, and the effort to implement id allocation was deemed not too high. It is also to the majority taste to deliver image descriptions with valid id.