Fix return value on malloc failure in tree_calculate_user_set.

Change-Id: I880dab43471b12c564909fbc00800b8f7a46575f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55747
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/crypto/x509v3/pcy_tree.c b/crypto/x509v3/pcy_tree.c
index 44ade30..7211e01 100644
--- a/crypto/x509v3/pcy_tree.c
+++ b/crypto/x509v3/pcy_tree.c
@@ -646,7 +646,7 @@
     if (!tree->user_policies) {
       tree->user_policies = sk_X509_POLICY_NODE_new_null();
       if (!tree->user_policies) {
-        return 1;
+        return 0;
       }
     }
     if (!sk_X509_POLICY_NODE_push(tree->user_policies, node)) {