[pitivi] viewer: Use overlay_stack only when it exists

[Alexandru Băluț <alexbalut src gnome org>]

commit e809f77f28c56a34c979661afdc284b27b818587
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Mon Jan 14 21:45:11 2019 +0100

    viewer: Use overlay_stack only when it exists

 pitivi/viewer/viewer.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/viewer/viewer.py b/pitivi/viewer/viewer.py
index 35a8f517..00c5b923 100644
--- a/pitivi/viewer/viewer.py
+++ b/pitivi/viewer/viewer.py
@@ -405,10 +405,10 @@ class ViewerContainer(Gtk.Box, Loggable):
 
         self.docked = False
         self.settings.viewerDocked = False
-        self.overlay_stack.enable_resize_status(False)
         self.remove(self.buttons_container)
         position = None
         if self.pipeline:
+            self.overlay_stack.enable_resize_status(False)
             position = self.pipeline.getPosition()
             self.pipeline.setState(Gst.State.NULL)
             self.remove(self.target)
@@ -446,10 +446,10 @@ class ViewerContainer(Gtk.Box, Loggable):
 
         self.docked = True
         self.settings.viewerDocked = True
-        self.overlay_stack.enable_resize_status(False)
 
         position = None
         if self.pipeline:
+            self.overlay_stack.enable_resize_status(False)
             position = self.pipeline.getPosition()
             self.pipeline.setState(Gst.State.NULL)
             self.external_vbox.remove(self.target)