[gnome-control-center] power: don't assume we have a Screen proxy when IIO proxy is ready

[Cosimo Cecchi <cosimoc src gnome org>]

commit db449dc49ea1145f0139562fc7d0797bfaaa16e9
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Tue Sep 8 10:02:00 2015 -0700

    power: don't assume we have a Screen proxy when IIO proxy is ready
    
    On panel construction, we trigger asynchronous creation of a GDBusProxy
    for the IIO sensors daemon and one for the Screen g-s-d interface.
    Since there's no guarantee we'll have the screen proxy ready by the time
    the IIO proxy is constructed, guard for (priv->screen_proxy != NULL), or
    we'll hit a critical.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754735

 panels/power/cc-power-panel.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)
---
diff --git a/panels/power/cc-power-panel.c b/panels/power/cc-power-panel.c
index b694989..4a96fe9 100644
--- a/panels/power/cc-power-panel.c
+++ b/panels/power/cc-power-panel.c
@@ -981,11 +981,14 @@ als_enabled_state_changed (CcPowerPanel *self)
   gboolean visible = FALSE;
   GVariant *v;
 
-  v = g_dbus_proxy_get_cached_property (self->priv->screen_proxy, "Brightness");
-  if (v != NULL)
+  if (priv->screen_proxy != NULL)
     {
-      has_brightness = g_variant_get_int32 (v) >= 0.0;
-      g_variant_unref (v);
+      v = g_dbus_proxy_get_cached_property (priv->screen_proxy, "Brightness");
+      if (v != NULL)
+        {
+          has_brightness = g_variant_get_int32 (v) >= 0.0;
+          g_variant_unref (v);
+        }
     }
 
   if (priv->iio_proxy != NULL)