BUGFIX: history link doesn't work on deleted posts

lib/guardian.rb

@@ -8,7 +8,7 @@ class Guardian
   include CategoryGuardian
   include PostGuardain
   include TopicGuardian
-    
+
   class AnonymousUser
     def blank?; true; end
     def admin?; false; end

lib/guardian/post_guardian.rb

@@ -104,7 +104,9 @@ module PostGuardain
   end
 
   def can_see_post_revision?(post_revision)
-    post_revision.present? && (is_staff? || can_see_post?(post_revision.post))
+    return false if post_revision.nil?
+    return true if SiteSetting.edit_history_visible_to_public
+    authenticated? && (is_staff? || can_see_post?(post_revision.post))
   end
 
   def can_vote?(post, opts={})