BUG/MEDIUM: ssl/sample: check output buffer size in aes_cbc_enc converter

BUG/MEDIUM: ssl/sample: check output buffer size in aes_cbc_enc converter

AES-CBC uses a 16-byte block size, and PKCS padding always adds at least
one byte (up to a full 16 bytes when input is already block-aligned), so
the encrypted output is always larger than the input. Without checking
that the output buffer can hold the padded result, encryption could
overflow it. Add a pre-encryption guard for block cipher (blksize > 1)
that rejects the operation when the output buffer is too small.

No backport needed.

Reported-by: Omkhar Arasaratnam <omkhar@linkedin.com>