[mutter] display: Don't crash on Alt-Escape.

[Florian Müllner <fmuellner src gnome org>]

commit b4888103a628faf910bf46472de9f58f75a8db4e
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Fri Jan 21 20:19:51 2011 -0500

    display: Don't crash on Alt-Escape.
    
    Fix a crash caused by 286160646bc711dba85171059c28c4d49803cc85, where
    we don't get a window when called from do_choose_window.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=640229

 src/core/display.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/src/core/display.c b/src/core/display.c
index bb13add..947be32 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -3581,7 +3581,10 @@ meta_display_begin_grab_op (MetaDisplay *display,
   display->grab_xwindow = grab_xwindow;
   display->grab_button = button;
   display->grab_mask = modmask;
-  display->grab_tile_mode = window->tile_mode;
+  if (window)
+    display->grab_tile_mode = window->tile_mode;
+  else
+    display->grab_tile_mode = META_TILE_NONE;
   display->grab_anchor_root_x = root_x;
   display->grab_anchor_root_y = root_y;
   display->grab_latest_motion_x = root_x;