[gnome-flashback] screenshot: initialize wm_window

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 1007ebf706d9a7eb1d46a4117b07fd3134475d11
Author: Antonio Ospite <ao2 ao2 it>
Date:   Wed Sep 28 18:34:13 2016 +0200

    screenshot: initialize wm_window
    
    https://bugzilla.gnome.org/show_bug.cgi?id=772133

 gnome-flashback/libscreenshot/gf-screenshot.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gnome-flashback/libscreenshot/gf-screenshot.c b/gnome-flashback/libscreenshot/gf-screenshot.c
index c9da2b5..abfebe5 100644
--- a/gnome-flashback/libscreenshot/gf-screenshot.c
+++ b/gnome-flashback/libscreenshot/gf-screenshot.c
@@ -598,6 +598,8 @@ take_screenshot_real (GfScreenshot    *screenshot,
     }
   else
     {
+      wm_window = NULL;
+
       frame_offset.left = 0;
       frame_offset.top = 0;
       frame_offset.right = 0;