[gupnp] Prevent critical if there's no system bus

[Jens Georg <jensgeorg src gnome org>]

commit 7507049677411547eed506ea76eb33539cb414e5
Author: Jens Georg <mail jensge org>
Date:   Sat May 10 18:32:18 2014 +0200

    Prevent critical if there's no system bus
    
    Found by Juan A. Suarez Romero <jasuarez igalia com>
    
    Signed-off-by: Jens Georg <mail jensge org>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=727709

 libgupnp/gupnp-context-manager.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgupnp/gupnp-context-manager.c b/libgupnp/gupnp-context-manager.c
index e766e93..31b711b 100644
--- a/libgupnp/gupnp-context-manager.c
+++ b/libgupnp/gupnp-context-manager.c
@@ -587,7 +587,7 @@ gupnp_context_manager_create (guint port)
                                                     NULL));
 
 #if defined(USE_NETWORK_MANAGER) || defined(USE_CONNMAN)
-        g_object_unref (system_bus);
+        g_clear_object (&system_bus);
 #endif
         return impl;
 }