[gnome-power-manager] Fix #627711 - Don't crash on systems which don't have XBACKLIGHT

[Richard Hughes <rhughes src gnome org>]

commit ac989105cc1f1c366863aa4430cc74250e1f46c6
Author: Chris Coulson <chris coulson canonical com>
Date:   Mon Aug 23 12:05:59 2010 +0100

    Fix #627711 - Don't crash on systems which don't have XBACKLIGHT

 src/gpm-brightness.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/gpm-brightness.c b/src/gpm-brightness.c
index 5453124..bff3411 100644
--- a/src/gpm-brightness.c
+++ b/src/gpm-brightness.c
@@ -518,6 +518,10 @@ gpm_brightness_foreach_screen (GpmBrightness *brightness, GpmXRandROp op)
 
 	g_return_val_if_fail (GPM_IS_BRIGHTNESS (brightness), FALSE);
 
+	/* Return immediately if we can't use XRandR */
+	if (!brightness->priv->has_extension)
+		return FALSE;
+
 	/* do for each screen */
 	length = brightness->priv->resources->len;
 	for (i=0; i<length; i++) {