[libwnck] core: Fix crash when reading pixmap icons that have no mask

[Vincent Untz <vuntz src gnome org>]

commit 77827ce14197637a7ac535ef5b3f3477d8a92b6a
Author: Vincent Untz <vuntz gnome org>
Date:   Thu Feb 3 17:48:54 2011 +0100

    core: Fix crash when reading pixmap icons that have no mask

 libwnck/xutils.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/libwnck/xutils.c b/libwnck/xutils.c
index 2551762..ec1fff8 100644
--- a/libwnck/xutils.c
+++ b/libwnck/xutils.c
@@ -1723,6 +1723,8 @@ try_pixmap_and_mask (Screen     *screen,
 
   if (surface && src_mask != None)
     mask_surface = _wnck_cairo_surface_get_from_pixmap (screen, src_mask);
+  else
+    mask_surface = NULL;
 
   _wnck_error_trap_pop ();