Fix history window not working

Fixes issue 4130

Change-Id: Ic6037c6a0716ff9c85c48e49716856e7f2faa90e
Reviewed-on: http://gerrit.dmdirc.com/1235
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Gregory Holmes <greg@dmdirc.com>

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

                          final FrameContainer<?> parent, final int numLines) {
         super("raw", title, title, Window.class, parent.getConfigManager());
 
-        this.parent = parent;
-
         WindowManager.addWindow(parent, this);
 
         final int frameBufferSize = IdentityManager.getGlobalConfig().getOptionInt(