[evince] page-action-widget: Fix runtime warnings on exit

[Carlos Garcia Campos <carlosgc src gnome org>]

commit 116d8bc1d3e26121bdeaf674bf3b87e068f7997c
Author: Caolán McNamara <caolanm redhat com>
Date:   Tue Nov 22 10:11:17 2016 +0000

    page-action-widget: Fix runtime warnings on exit
    
    There's a warning on exit of evince sometimes, doc_model has been zeroed
    by ev_view_accessible_finalize() already before this is called during teardown.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=774833

 libmisc/ev-page-action-widget.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/libmisc/ev-page-action-widget.c b/libmisc/ev-page-action-widget.c
index 2c14c7e..cb40066 100644
--- a/libmisc/ev-page-action-widget.c
+++ b/libmisc/ev-page-action-widget.c
@@ -262,8 +262,10 @@ ev_page_action_widget_set_document (EvPageActionWidget *action_widget,
         }
 
         if (action_widget->signal_id > 0) {
-                g_signal_handler_disconnect (action_widget->doc_model,
-                                             action_widget->signal_id);
+                if (action_widget->doc_model != NULL) {
+                        g_signal_handler_disconnect (action_widget->doc_model,
+                                                     action_widget->signal_id);
+                }
                 action_widget->signal_id = 0;
         }