Run X509_print in the certificate fuzzer.

Given the error handling issues in the previous CL, we'll probably be
chasing down bugs in there for a while.

Change-Id: I7a219e0fe2496f602d38b4bd0fcd5585ebd72cb7
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49046
Reviewed-by: Adam Langley <agl@google.com>

fuzz/cert.cc

@@ -26,6 +26,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
     uint8_t *der = NULL;
     i2d_X509(x509, &der);
     OPENSSL_free(der);
+
+    BIO *bio = BIO_new(BIO_s_mem());
+    X509_print(bio, x509);
+    BIO_free(bio);
   }
   X509_free(x509);
   ERR_clear_error();