tree_print: check for NULL after allocating err

Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NMatt Caswell <matt@openssl.org>

crypto/x509v3/pcy_tree.c

@@ -101,6 +101,8 @@ static void tree_print(char *str, X509_POLICY_TREE *tree,
 	int i;
 	BIO *err;
 	err = BIO_new_fp(stderr, BIO_NOCLOSE);
+	if (err == NULL)
+		return;
 	if (!curr)
 		curr = tree->levels + tree->nlevel;
 	else