secp256k1.c: secp256k1_ecdsa_signature_serialize_der - use constant when initializing sigout with size
secp256k1.c: secp256k1_ecdsa_signature_serialize_der - use constant when initializing sigout with size

afk11/secp256k1-php,afk11/secp256k1-php,afk11/secp256k1-php,afk11/secp256k1-php,afk11/secp256k1-php