Fix pgcrypto compilation with OpenSSL 1.1.0.

Was broken by the switch to using OpenSSL's EVP interface for ciphers, in
commit 5ff4a67f.

Reported by Andres Freund. Fix by Michael Paquier with some kibitzing by me.

Discussion: https://www.postgresql.org/message-id/20161201014826.ic72tfkahmevpwz7@alap3.anarazel.de

contrib/pgcrypto/pgp-encrypt.c

@@ -219,6 +219,8 @@ encrypt_free(void *priv)
 {
 	struct EncStat *st = priv;
 
+	if (st->ciph)
+		pgp_cfb_free(st->ciph);
 	px_memset(st, 0, sizeof(*st));
 	px_free(st);
 }