fix GLib-GObject-CRITICAL **: invalid cast from 'GtkImage' to 'GtkLabel'

Change-Id: I29024237cc2d92d16433cf432f87e2b42107a487
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/168630
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolan.mcnamara@collabora.com>
diff --git a/cui/uiconfig/ui/numberingoptionspage.ui b/cui/uiconfig/ui/numberingoptionspage.ui
index e9d57e6..5e6a112 100644
--- a/cui/uiconfig/ui/numberingoptionspage.ui
+++ b/cui/uiconfig/ui/numberingoptionspage.ui
@@ -359,6 +359,7 @@
                        <property name="receives-default">False</property>
                        <property name="xalign">0</property>
                        <property name="draw-indicator">True</property>
                        <property name="label" translatable="no"></property>
                        <child>
                          <placeholder/>
                        </child>