Limit ASN.1 constructed types recursive definition depth

Limit ASN.1 constructed types recursive definition depth

Constructed types with a recursive definition (such as can be found in
PKCS7) could eventually exceed the stack given malicious input with
excessive recursion. Therefore we limit the stack depth.

CVE-2018-0739

Credit to OSSFuzz for finding this issue.

Reviewed-by: Rich Salz <rsalz@openssl.org>