[pitivi] viewer: Silence Gtk warning

[Alexandru Băluț <alexbalut src gnome org>]

commit 129b638d70ce99037d80401e2609c17352344494
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sun May 29 14:46:02 2016 +0200

    viewer: Silence Gtk warning
    
    Differential Revision: https://phabricator.freedesktop.org/D946

 pitivi/viewer/viewer.py |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/pitivi/viewer/viewer.py b/pitivi/viewer/viewer.py
index a16862c..b57a234 100644
--- a/pitivi/viewer/viewer.py
+++ b/pitivi/viewer/viewer.py
@@ -507,11 +507,13 @@ class ViewerWidget(Gtk.AspectFrame, Loggable):
         self.set_property("ratio", float(ratio))
 
     def do_get_preferred_width(self):
+        Gtk.AspectFrame.do_get_preferred_width(self)
         # Do not let a chance for Gtk to choose video natural size
         # as we want to have full control
         return 0, 1
 
     def do_get_preferred_height(self):
+        Gtk.AspectFrame.do_get_preferred_height(self)
         # Do not let a chance for Gtk to choose video natural size
         # as we want to have full control
         return 0, 1