[gnome-documents] preview: Check if this._jobFind is null

[Alessandro Bono <abono src gnome org>]

commit f5b2047060d9a071a942125d0f837dbc19310bd6
Author: Alessandro Bono <abono gnome org>
Date:   Sun Jan 3 14:11:33 2016 +0100

    preview: Check if this._jobFind is null
    
    Fallout from cd6d7c76ddf063fe0f285044c06ced0ce45e97d7
    
    https://bugzilla.gnome.org/show_bug.cgi?id=759248

 src/preview.js |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/preview.js b/src/preview.js
index ddac1e3..4158105 100644
--- a/src/preview.js
+++ b/src/preview.js
@@ -569,9 +569,11 @@ const PreviewView = new Lang.Class({
 
             this.set_visible_child_full('view', Gtk.StackTransitionType.NONE);
         } else {
-            if (!this._jobFind.is_finished())
-                this._jobFind.cancel();
-            this._jobFind = null;
+           if (this._jobFind) {
+               if (!this._jobFind.is_finished())
+                   this._jobFind.cancel();
+               this._jobFind = null;
+           }
         }
     },