CVE-2026-12817: OpenPGP AEAD decryption skips final tag on chunk-aligned data

Affects Bouncy Castle for Java before 1.85. OpenPGP AEAD decryption verifies the final tag only when the last chunk is shorter than the chunk length. For chunk-aligned data the stream reports clean EOF without calling doFinal(), and AEAD verification always reports success, so nothing detects the omission. An attacker who controls the ciphertext can drop trailing chunks and the final tag, adjust the unauthenticated outer packet length, and have truncated plaintext accepted as authentic.