unlockDialog: Show clock when canceling or failing auth

There is still a problem of focus not going to the entry after the
first cancel, but it seems to work fine otherwise.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/872

js/ui/unlockDialog.js

@@ -591,6 +591,7 @@ var UnlockDialog = GObject.registerClass({
     }
 
     _fail() {
+        this._showClock();
         this.emit('failed');
     }