V1Plugin.Decrypt panics on empty ciphertext (Remote DoS)

Component: pkg/plugin/plugin.go:179 Affected Version: aws-encryption-provider @ 4341c70 (all versions) Found by: Fuzz testing (FuzzV1Decrypt, seed#0: empty []byte{})

Summary

V1Plugin.Decrypt() accesses request.Cipher[0] without checking that the slice is non-empty. Sending a DecryptRequest with empty or nil Cipher field causes an unrecoverable index out of range panic that crashes the entire gRPC server process.