Old version of libglade crashes if there is not an id in the object class

Author: antenore

remmina/ui/remmina_main.glade

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.20.0 
+<!-- Generated with glade 3.20.0
 
 Remmina - The GTK+ Remmina Remote Desktop Client
 Copyright (C) Antenore Gatta & Giovanni Panozzo 2014-2018
@@ -731,7 +731,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
             <property name="margin_right">16</property>
             <property name="orientation">vertical</property>
             <child>
-              <object class="GtkSeparator">
+              <object class="GtkSeparator" id="ustat_separator">
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
               </object>