[gnome-boxes] display-page: Drop ref on display upon its removal

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit a17fcbfb585234b7a451396a4c58e4786d746f7c
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Tue May 12 17:51:50 2015 +0100

    display-page: Drop ref on display upon its removal
    
    Once DisplayPage is told to remove the display, it should be giving up
    its reference to the display being removed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746800

 src/display-page.vala |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/display-page.vala b/src/display-page.vala
index 4b2a2ef..9741ab8 100644
--- a/src/display-page.vala
+++ b/src/display-page.vala
@@ -188,6 +188,7 @@ private class Boxes.DisplayPage: Gtk.Box {
             display.disconnect (keyboard_grabbed_id);
             keyboard_grabbed_id = 0;
         }
+        display = null;
 
         var widget = event_box.get_child ();