Check public key is not NULL.

CVE-2015-0288
PR#3708

Reviewed-by: Matt Caswell <matt@openssl.org>
(cherry picked from commit 28a00bcd8e)

crypto/x509/x509_req.c

@@ -91,6 +91,8 @@ X509_REQ *X509_to_X509_REQ(X509 *x, EVP_PKEY *pkey, const EVP_MD *md)
         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)