[gnome-shell/gnome-3-20] loginDialog: fix cancel button in ask for username mode

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 15e727e1745ad1c309eb1dafc20b1c0d1b249ba1
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Sat Sep 10 12:55:20 2016 -0500

    loginDialog: fix cancel button in ask for username mode
    
    If the user clicks Not Listed? to enter ask for username mode, clicks
    cancel, and then attempts to log in via the user list, the user will see
    "Authentication failed" after correctly typing the password, and then
    will become stuck in an empty screen with just the gray noise background.
    
    The problem is, we forgot to disconnect from the signal that's waiting
    for the next button to be pressed on the username entry screen. Since
    the signal handler that executes here is expecting the username to be
    input, and isn't prepared for us to have switched back to user list,
    various bad things happen. We try to start two gdm-password
    conversations at once, for instance, one using the user's password as
    the username. I stopped investigating here, because it's easy to fix by
    disconnecting from the signal at the right time.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=770328

 js/gdm/loginDialog.js |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/js/gdm/loginDialog.js b/js/gdm/loginDialog.js
index 46eeb83..d88e50f 100644
--- a/js/gdm/loginDialog.js
+++ b/js/gdm/loginDialog.js
@@ -804,6 +804,11 @@ const LoginDialog = new Lang.Class({
 
         this._user = null;
 
+        if (this._nextSignalId) {
+            this._authPrompt.disconnect(this._nextSignalId);
+            this._nextSignalId = 0;
+        }
+
         if (beginRequest == AuthPrompt.BeginRequestType.PROVIDE_USERNAME) {
             if (!this._disableUserList)
                 this._showUserList();