gtklistboxrow: propagate in the draw vfunc

So objects connected by g_signal_connect_after actually get
the signal.
This was causing an issue in the dnd highlight, since there
a cairo rectangle is draw using g_signal_connect_after on the draw
signal.

gtk/gtklistbox.c

@@ -3089,7 +3089,7 @@ gtk_list_box_row_draw (GtkWidget *widget,
 
   GTK_WIDGET_CLASS (gtk_list_box_row_parent_class)->draw (widget, cr);
 
-  return TRUE;
+  return GDK_EVENT_PROPAGATE;
 }
 
 static void