NPE if using CachingMostRecentProvider to decrypt records without "amzn-ddb-meta-id"

### Problem:

If a user attempts to use a CachingMostRecentProvider to decrypt a record that *does* contain a mat-desc, but that mat-desc does not contain the key value "amzn-ddb-meta-id," they get an NPE. This can happen if a user tries to encrypt with another one of our providers then decrypt with the CachingMostRecentProvider.

### Solution:

Instead, users should get a more friendly error that decryption was unable to succeed.

### Out of scope:

The CachingMostRecentProvider is not intended to interoperate with other providers.

[//]: # (NOTE: If you believe this might be a security issue, please email aws-security@amazon.com instead of creating a GitHub issue. For more details, see the AWS Vulnerability Reporting Guide: https://aws.amazon.com/security/vulnerability-reporting/ )

Comienza por la ruta de descifrado de CachingMostRecentProvider descrita en el issue y sigue cómo se maneja un mat-desc sin "amzn-ddb-meta-id". Reproduce el caso usando un registro cifrado por otro Provider y verifica después que el descifrado falle con un error claro en lugar de producir una NPE.

Escrito por el modelo de indexación a partir del texto del issue.