[krb5-auth-dialog] credentials_expiring_real: check if kcontext is valid

[Guido Günther <guidog src gnome org>]

commit 23ba826890d60c3c556a8d1a021e97b8d3fb416c
Author: Guido Günther <agx sigxcpu org>
Date:   Fri Jul 7 09:10:37 2017 +0200

    credentials_expiring_real: check if kcontext is valid
    
    othewise we might crash when the credentials_expiring_once fires but
    we're already shutting down.
    
    Reference: https://bugs.launchpad.net/bugs/1700468

 src/ka-kerberos.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/src/ka-kerberos.c b/src/ka-kerberos.c
index 0fbaf88..d17a63e 100644
--- a/src/ka-kerberos.c
+++ b/src/ka-kerberos.c
@@ -218,6 +218,9 @@ credentials_expiring_real (KaApplet *applet)
     krb5_timestamp now;
     gboolean retval = FALSE;
 
+    if (!kcontext_valid)
+        return retval;
+
     memset (&my_creds, 0, sizeof (my_creds));
     ka_applet_set_tgt_renewable (applet, FALSE);
     if (!ka_get_tgt_from_ccache (kcontext, &my_creds)) {
@@ -938,8 +941,8 @@ static gboolean
 ka_krb5_context_free ()
 {
     if (kcontext_valid) {
-        krb5_free_context (kcontext);
         kcontext_valid = FALSE;
+        krb5_free_context (kcontext);
     }
     return TRUE;
 }