NEW Hide subsite selector dropdown if no subsites have been created yet

Note that "Main site" is always included in the list of subsites, even though it is not an actual record

templates/SilverStripe/Admin/LeftAndMain_Menu.ss

@@ -5,7 +5,7 @@
         <% include SilverStripe\\Admin\\LeftAndMain_MenuLogo %>
         <% include SilverStripe\\Admin\\LeftAndMain_MenuStatus %>
 
-        <% if $ListSubsites %>
+        <% if $ListSubsites.Count > 1 %>
             <% include SilverStripe\\Subsites\\Controller\\SubsiteXHRController_subsitelist %>
         <% end_if %>
     </div>