[evince] history: Don't assume EvLink has always a valid EvLinkAction

[Germán Poo-Caamaño <gpoo src gnome org>]

commit 6d3f7570c76941d78b79906488ef862359de5369
Author: Nelson Benítez León <nbenitezl gmail com>
Date:   Mon Sep 3 06:41:15 2018 -0700

    history: Don't assume EvLink has always a valid EvLinkAction
    
    Fixes following critical when navigating history with mouse
    back/forward buttons:
    
    EvinceDocument-CRITICAL **: ev_link_action_equal: assertion 'EV_IS_LINK_ACTION (b)' failed
    
    Parially fixes #810 (5/5)

 shell/ev-history.c | 7 ++++++-
 shell/ev-window.c  | 6 +++++-
 2 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/shell/ev-history.c b/shell/ev-history.c
index a0b33d18..9aa156f5 100644
--- a/shell/ev-history.c
+++ b/shell/ev-history.c
@@ -263,10 +263,15 @@ static gint
 compare_link (EvLink *a,
               EvLink *b)
 {
+        EvLinkAction *aa, *bb;
+
         if (a == b)
                 return 0;
 
-        return ev_link_action_equal (ev_link_get_action (a), ev_link_get_action (b)) ? 0 : 1;
+        aa = ev_link_get_action (a);
+        bb = ev_link_get_action (b);
+
+        return (aa && bb && ev_link_action_equal (aa, bb)) ? 0 : 1;
 }
 
 /*
diff --git a/shell/ev-window.c b/shell/ev-window.c
index 67f67190..a64ca238 100644
--- a/shell/ev-window.c
+++ b/shell/ev-window.c
@@ -882,6 +882,7 @@ find_link_cb (GtkTreeModel  *tree_model,
              LinkTitleData *data)
 {
        EvLink *link;
+       EvLinkAction *a, *b;
        gboolean retval = FALSE;
 
        gtk_tree_model_get (tree_model, iter,
@@ -890,7 +891,10 @@ find_link_cb (GtkTreeModel  *tree_model,
        if (!link)
                return retval;
 
-       if (ev_link_action_equal (ev_link_get_action (data->link), ev_link_get_action (link))) {
+       a = ev_link_get_action (data->link);
+       b = ev_link_get_action (link);
+
+       if (a && b && ev_link_action_equal (a, b)) {
                data->link_title = ev_link_get_title (link);
                retval = TRUE;
        }