Revisions: Immediately do a disabled button check on `ready()`.

Solves the issue of Prev/Next buttons not being disabled on initial load, when routing to an extremity.

See #24425.

git-svn-id: http://core.svn.wordpress.org/trunk@24661 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/revisions.js

@@ -664,10 +664,11 @@ window.wp = window.wp || {};
 
 		initialize: function() {
 			this.$el.html( this.template() );
+			this.listenTo( this.model, 'update:revisions', this.disabledButtonCheck );
 		},
 
 		ready: function() {
-			this.listenTo( this.model, 'update:revisions', this.disabledButtonCheck );
+			this.disabledButtonCheck();
 		},
 
 		// Go to a specific modelindex, taking into account RTL mode.