Have fuzz/cert.cc also call X509_get_pubkey.

crypto/x509 parses the SPKI on-demand, so we weren't actually exercising the
SPKI code.

Change-Id: I2e16045bd35dbe04d4b8d8b45939c8885e09a550
Reviewed-on: https://boringssl-review.googlesource.com/7161
Reviewed-by: Adam Langley <agl@google.com>

fuzz/cert.cc

@@ -2,6 +2,11 @@
 
 extern "C" int LLVMFuzzerTestOneInput(uint8_t *buf, size_t len) {
   const uint8_t *bufp = buf;
-  X509_free(d2i_X509(NULL, &bufp, len));
+  X509 *x509 = d2i_X509(NULL, &bufp, len);
+  if (x509 != NULL) {
+    /* Also extract the public key. */
+    EVP_PKEY_free(X509_get_pubkey(x509));
+  }
+  X509_free(x509);
   return 0;
 }