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

从 src/main/java/com/amazonaws/encryptionsdk/model/CiphertextType.java 开始，具体检查 CiphertextType.deserialize 及其关联行。检查对于不是有效 ciphertext 类型 ID 的字节的行为；当无效输入抛出错误而不是返回 null，并且有覆盖该行为的测试时，即视为完成。

由索引模型根据 Issue 内容生成。