DockWindow missing builder dispose.

Change-Id: I020ce8efc9d2315a0d6d72914976c2a01b893d12
diff --git a/vcl/source/window/dockwin.cxx b/vcl/source/window/dockwin.cxx
index d6ed20d..1a5206b 100644
--- a/vcl/source/window/dockwin.cxx
+++ b/vcl/source/window/dockwin.cxx
@@ -486,6 +486,7 @@ void DockingWindow::dispose()
    mpFloatWin.clear();
    mpOldBorderWin.clear();
    mpDialogParent.clear();
    disposeBuilder();
    Window::dispose();
}