[gnome-shell/T29763: 215/249] fixup! payg: Add success screen

[Matthew Leeds <mwleeds src gnome org>]

commit 8e1edb516da463cf2610b38ad626e23196ba240c
Author: Matthew Leeds <matthew leeds endlessm com>
Date:   Mon Apr 13 17:28:10 2020 -0700

    fixup! payg: Add success screen
    
    Fix "JS ERROR: this._dialog is null" in the log after a valid code is
    applied using the tray applet.

 js/ui/screenShield.js | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index d7523181a6..b3848d7d69 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -155,6 +155,11 @@ var ScreenShield = class {
                 return;
             }
 
+            // The time may have been extended using the tray applet from a
+            // logged in session.
+            if (this._dialog === null)
+                return;
+
             // Take the dialog instance and wait for the success message to be shown
             this._dialog.connect('success-message-shown', () => {
                 // A new valid code unlocked the machine and user has no