[libwnck] utils: fix compilation warning (thus error) if XRes is missing

[Marco Trevisan <marcotrevi src gnome org>]

commit edaaa25ab65e95fdaae324e8e06be99594d60387
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Jun 29 01:31:01 2017 +0200

    utils: fix compilation warning (thus error) if XRes is missing

 libwnck/util.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)
---
diff --git a/libwnck/util.c b/libwnck/util.c
index 7ee54fa..d90f585 100644
--- a/libwnck/util.c
+++ b/libwnck/util.c
@@ -106,18 +106,17 @@ _wnck_print_resource_usage (WnckResourceUsage *usage)
 static WnckExtStatus
 wnck_init_resource_usage (GdkDisplay *gdisplay)
 {
-  int event, error;
-  Display *xdisplay;
   WnckExtStatus status;
 
-  xdisplay = GDK_DISPLAY_XDISPLAY (gdisplay);
-
   status = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (gdisplay),
                                                "wnck-xres-status"));
 
   if (status == WNCK_EXT_UNKNOWN)
     {
 #ifdef HAVE_XRES
+      Display *xdisplay = GDK_DISPLAY_XDISPLAY (gdisplay);
+      int event, error;
+
       if (!XResQueryExtension (xdisplay, &event, &error))
         status = WNCK_EXT_MISSING;
       else