[gtk+] Check if XRRGetOutputInfo returned a null pointer.

[Matthias Clasen <matthiasc src gnome org>]

commit f3f998efd7538a338ca2959c21a93ec633e17737
Author: fiddlerwoaroof <fiddlerwoaroof+gb gmail com>
Date:   Thu Mar 3 10:30:00 2016 -0500

    Check if XRRGetOutputInfo returned a null pointer.
    
    Fixes bug 763023: in certain circumstances, XRRGetOutputInfo will return
    a null pointer.  This commit adds a check to detect and handle this
    return value.

 gdk/x11/gdkscreen-x11.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gdk/x11/gdkscreen-x11.c b/gdk/x11/gdkscreen-x11.c
index 82b8aa2..063b597 100644
--- a/gdk/x11/gdkscreen-x11.c
+++ b/gdk/x11/gdkscreen-x11.c
@@ -653,6 +653,9 @@ init_randr15 (GdkScreen *screen)
         XRRGetOutputInfo (x11_screen->xdisplay, resources, output);
       GdkX11Monitor monitor;
 
+      if (output_info == NULL)
+        continue;
+
       /* Non RandR1.2+ X driver have output name "default" */
       randr12_compat |= !g_strcmp0 (output_info->name, "default");