Restore use of guard which was accidently removed in a previous clean up

Clean up was in 8b888234
diff --git a/java/org/apache/tomcat/util/modeler/Registry.java b/java/org/apache/tomcat/util/modeler/Registry.java
index 7ef9ad7..e98a598 100644
--- a/java/org/apache/tomcat/util/modeler/Registry.java
+++ b/java/org/apache/tomcat/util/modeler/Registry.java
@@ -141,6 +141,7 @@
             } else {
                 registry = new Registry();
             }
+            registry.guard = guard;
         }
         if (registry.guard != null && registry.guard != guard) {
             return null;