Fix a failure to NULL a pointer freed on error.

Inspired by BoringSSL commit 517073cd4b by Eric Roman <eroman@chromium.org>

CVE-2015-0209

Reviewed-by: Emilia Käsper <emilia@openssl.org>

Author: mattcaswell

crypto/ec/ec_asn1.c

@@ -1014,8 +1014,6 @@ EC_KEY *d2i_ECPrivateKey(EC_KEY **a, const unsigned char **in, long len)
             ECerr(EC_F_D2I_ECPRIVATEKEY, ERR_R_MALLOC_FAILURE);
             goto err;
         }
-        if (a)
-            *a = ret;
     } else
         ret = *a;
 
@@ -1067,10 +1065,12 @@ EC_KEY *d2i_ECPrivateKey(EC_KEY **a, const unsigned char **in, long len)
         }
     }
 
+    if (a)
+        *a = ret;
     ok = 1;
  err:
     if (!ok) {
-        if (ret)
+        if (ret && (a == NULL || *a != ret))
             EC_KEY_free(ret);
         ret = NULL;
     }