[metacity] xrender: avoid a critical

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 37a7eaf5a9368365562b55df6818195f0da1456f
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Mar 12 13:16:42 2017 +0200

    xrender: avoid a critical

 src/compositor/meta-compositor-xrender.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/compositor/meta-compositor-xrender.c b/src/compositor/meta-compositor-xrender.c
index ee88832..bd5d788 100644
--- a/src/compositor/meta-compositor-xrender.c
+++ b/src/compositor/meta-compositor-xrender.c
@@ -2601,7 +2601,7 @@ meta_compositor_xrender_finalize (GObject *object)
       free_win (xrender, cw, TRUE);
     }
   g_list_free (xrender->windows);
-  g_hash_table_destroy (xrender->windows_by_xid);
+  g_clear_pointer (&xrender->windows_by_xid, g_hash_table_destroy);
 
   if (xrender->root_picture)
     XRenderFreePicture (xdisplay, xrender->root_picture);