[mutter/wayland] Fix the build with -Werror=maybe-uninitialized

[Matthias Clasen <matthiasc src gnome org>]

commit f4f529385ab0c397caa7816435c3e203acb3686e
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Mar 27 14:58:20 2014 -0400

    Fix the build with -Werror=maybe-uninitialized
    
    gcc can't really know that the condition won't change between
    the first if and the second, so help it out by initializing
    the variable up top.

 src/compositor/compositor.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index 54fcd44..075d4ac 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -517,7 +517,7 @@ meta_compositor_manage (MetaCompositor *compositor)
   MetaDisplay *display = compositor->display;
   Display *xdisplay = display->xdisplay;
   MetaScreen *screen = display->screen;
-  Window xwin;
+  Window xwin = 0;
   gint width, height;
   MetaWaylandCompositor *wayland_compositor;