check for error when creating PKCS#8 structure

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

crypto/pem/pem_pk8.c

@@ -139,6 +139,8 @@ static int do_pk8pkey(BIO *bp, EVP_PKEY *x, int isder, int nid,
         if (kstr == buf)
             OPENSSL_cleanse(buf, klen);
         PKCS8_PRIV_KEY_INFO_free(p8inf);
+        if (p8 == NULL)
+            return 0;
         if (isder)
             ret = i2d_PKCS8_bio(bp, p8);
         else