[krb5-auth-dialog] krb5_principal_compare crashes on NULL arguments

[Guido Günther <guidog src gnome org>]

commit 9acb30e12410b5fa6f08d5f38a6ddecbd06d3139
Author: Petter Reinholdtsen <pere hungry com>
Date:   Thu Jul 4 09:32:18 2013 +0200

    krb5_principal_compare crashes on NULL arguments
    
    Debian Bug #714825

 src/ka-kerberos.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/ka-kerberos.c b/src/ka-kerberos.c
index db5cddd..0867234 100644
--- a/src/ka-kerberos.c
+++ b/src/ka-kerberos.c
@@ -221,8 +221,10 @@ credentials_expiring_real (KaApplet *applet)
     }
 
     /* copy principal from cache if any */
-    if (krb5_principal_compare (kcontext, my_creds.client, kprincipal)) {
-        krb5_free_principal (kcontext, kprincipal);
+    if (kprincipal == NULL ||
+        krb5_principal_compare (kcontext, my_creds.client, kprincipal)) {
+        if (kprincipal)
+            krb5_free_principal (kcontext, kprincipal);
         krb5_copy_principal (kcontext, my_creds.client, &kprincipal);
     }
     creds_expiry = my_creds.times.endtime;