Avoid NullPointerException

...when dispose is called without a preceding call to initialize (as would
happen with an improved CppunitTest_services)

Change-Id: Ic632d736ecb27509b092ef526cf0dfc964023663
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/150576
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

scripting/java/Framework/com/sun/star/script/framework/security/SecurityDialog.java

@@ -515,10 +515,12 @@ public class SecurityDialog extends WeakBase implements
 
     public void dispose() {
 
-        XComponent xComponent =
-            UnoRuntime.queryInterface(XComponent.class, _xDialog);
+        if (_xDialog != null) {
+            XComponent xComponent =
+                UnoRuntime.queryInterface(XComponent.class, _xDialog);
 
-        xComponent.dispose();
+            xComponent.dispose();
+        }
     }
 
     public void addEventListener(com.sun.star.lang.XEventListener xListener) {