[gnome-tetravex] Fix window size increase under GTK+ 3.20

[Mario Wenzel <mariowenzel src gnome org>]

commit c80289d751afa1679b10b1b537f2ba4ea75721ef
Author: Mario Wenzel <maweki gmail com>
Date:   Mon Feb 15 18:37:24 2016 +0100

    Fix window size increase under GTK+ 3.20

 src/gnome-tetravex.vala |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/src/gnome-tetravex.vala b/src/gnome-tetravex.vala
index 49bea3f..aea20b6 100644
--- a/src/gnome-tetravex.vala
+++ b/src/gnome-tetravex.vala
@@ -196,8 +196,7 @@ public class Tetravex : Gtk.Application
     {
         if (is_maximized || is_tiled)
             return;
-        window_width = allocation.width;
-        window_height = allocation.height;
+        window.get_size (out window_width, out window_height);
     }
 
     private bool window_state_event_cb (Gdk.EventWindowState event)