CiphertextType.deserialize should throw an error if it encounters an invalid type

Currently, if `CiphertextType.deserialize` is called with a byte containing anything other than a valid ciphertext type ID, it will return `null`. This seems like the wrong behavior to me.

https://github.com/aws/aws-encryption-sdk-java/blob/master/src/main/java/com/amazonaws/encryptionsdk/model/CiphertextType.java#L71-L75

Start with src/main/java/com/amazonaws/encryptionsdk/model/CiphertextType.java, specifically CiphertextType.deserialize and the linked lines. Check the behavior for bytes that are not valid ciphertext type IDs; done means invalid input throws an error instead of returning null, with coverage for that behavior.

Written by the indexing model from the issue text.