[zenity] Fix GLib critical messages

[Arx Henrique Pereira da Cruz <arxcruz src gnome org>]

commit 160f0442c62579b79b15f953a9e6766a833952fd
Author: Arx Cruz <arxcruz gnome org>
Date:   Fri May 29 14:29:12 2015 +0200

    Fix GLib critical messages

 src/notification.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/notification.c b/src/notification.c
index 2bdd05b..a4355a1 100644
--- a/src/notification.c
+++ b/src/notification.c
@@ -342,9 +342,11 @@ zenity_notification (ZenityData *data, ZenityNotificationData *notification_data
                                     NULL);
 
     /* set the notification hints for the displayed notification */
-    notification_hints = zenity_notification_parse_hints_array (notification_data->notification_hints);
-    zenity_notification_set_hints(notification, notification_hints);
-    g_hash_table_unref (notification_hints);
+    if (notification_data->notification_hints != NULL) {
+      notification_hints = zenity_notification_parse_hints_array (notification_data->notification_hints);
+      zenity_notification_set_hints(notification, notification_hints);
+      g_hash_table_unref (notification_hints);
+    }
 
     /* Show icon and wait */
     error = NULL;