Check public key is not NULL.

CVE-2015-0288
PR#3708

(Imported from upstream's 28a00bcd8e318da18031b2ac8778c64147cd54f9.)

Change-Id: I6d60691da4c6860f87c753c065e93e9d0704aba9
Reviewed-on: https://boringssl-review.googlesource.com/3750
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/x509/x509_req.c b/crypto/x509/x509_req.c
index daaedb6..2732d6e 100644
--- a/crypto/x509/x509_req.c
+++ b/crypto/x509/x509_req.c
@@ -92,6 +92,8 @@
 		goto err;
 
 	pktmp = X509_get_pubkey(x);
+	if (pktmp == NULL)
+		goto err;
 	i=X509_REQ_set_pubkey(ret,pktmp);
 	EVP_PKEY_free(pktmp);
 	if (!i) goto err;