demos/scale: fix blank subsamples spin box

It now shows the initial value of 4 when the demo is started

Signed-off-by: Bill Spitzak <spitzak@gmail.com>
Reviewed-by: Søren Sandmann <soren.sandmann@gmail.com>
diff --git a/demos/scale.ui b/demos/scale.ui
index ee985dd..f6f6e89 100644
--- a/demos/scale.ui
+++ b/demos/scale.ui
@@ -301,6 +301,7 @@
                       <object class="GtkSpinButton" id="subsample_spin_button">
                         <property name="visible">True</property>
 			<property name="adjustment">subsample_adjustment</property>
+			<property name="value">4</property>
                       </object>
                       <packing>
                         <property name="left_attach">1</property>