[gnome-control-center] power: Fix possible crash if up_client_get_devices() fails

[Bastien Nocera <hadess src gnome org>]

commit d2c0b66275683169395616d19fce8d4dacfe84bf
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Jun 17 10:53:07 2015 +0200

    power: Fix possible crash if up_client_get_devices() fails
    
    up_client_get_devices() can fail if upower crashes or isn't available.
    Make sure not to crash ourselves by handling NULL return values as we do
    later in the loop.
    
    See https://bugzilla.redhat.com/show_bug.cgi?id=1175421
    
    https://bugzilla.gnome.org/show_bug.cgi?id=751095

 panels/power/cc-power-panel.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/panels/power/cc-power-panel.c b/panels/power/cc-power-panel.c
index f30b90e..500649a 100644
--- a/panels/power/cc-power-panel.c
+++ b/panels/power/cc-power-panel.c
@@ -1136,7 +1136,7 @@ set_ac_battery_ui_mode (CcPowerPanel *self)
   UpDeviceKind kind;
 
   devices = up_client_get_devices (self->priv->up_client);
-  g_debug ("got %d devices from upower\n", devices->len);
+  g_debug ("got %d devices from upower\n", devices ? devices->len : 0);
 
   for (i = 0; devices != NULL && i < devices->len; i++)
     {