Don't access protected vars

Change-Id: Ia332992e0259e88511b60cf565c7b09f5fc4e796
Reviewed-on: http://gerrit.dmdirc.com/2123
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/addons/logging/HistoryWindow.java

@@ -68,13 +68,12 @@ public class HistoryWindow extends FrameContainer {
     @Override
     public void windowClosed() {
         // 7: Remove any references to the window and parents
-        parent = null; // NOPMD
     }
 
     /** {@inheritDoc} */
     @Override
     public Server getServer() {
-        return parent == null ? null : parent.getServer();
+        return getParent() == null ? null : getParent().getServer();
     }
 
 }