Fix writable frame container harness

Change-Id: I07bc51e40d5775439e6abf02bb7b0b8719675374
Reviewed-on: http://gerrit.dmdirc.com/924
Reviewed-by: Gregory Holmes <greg@dmdirc.com>
Automatic-Compile: Gregory Holmes <greg@dmdirc.com>

test/com/dmdirc/harness/TestWritableFrameContainer.java

@@ -61,6 +61,10 @@ public class TestWritableFrameContainer extends WritableFrameContainer {
         WindowManager.removeWindow(window);
     }
 
+    public void windowClosed() {
+        // DO nothing
+    }
+
     public Server getServer() {
         return null;
     }