Report ReferenceSchema Event only when it match the schema

This PR aims to report the ReferecenceSchema event only when the schema is matching against the event.

Author: afranzi

core/src/main/java/org/everit/json/schema/ValidatingVisitor.java

@@ -133,7 +133,7 @@ void visitReferenceSchema(ReferenceSchema referenceSchema) {
         if (failure != null) {
             failureReporter.failure(failure);
         }
-        if (validationListener != null) {
+        else if (validationListener != null) {
             validationListener.schemaReferenced(new SchemaReferencedEvent(referenceSchema, subject, referredSchema));
         }
     }