[gnome-shell] ScreenShield: fix regression from 2c627cad

[Giovanni Campagna <gcampagna src gnome org>]

commit b3b847faddf34ff46789ba51320d522a14ae4b42
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Thu Aug 16 19:19:55 2012 +0200

    ScreenShield: fix regression from 2c627cad
    
    A method was renamed but one call site was forgotten.

 js/ui/screenShield.js |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index 7601340..332571f 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -583,7 +583,7 @@ const ScreenShield = new Lang.Class({
             // The dialog must be kept alive,
             // so immediately go back to it
             // This will also reset _isLocked
-            this._showUnlockDialog(false);
+            this._ensureUnlockDialog();
             return;
         }