Fix error on Linux with Ruby 1.8

fzf

@@ -10,7 +10,7 @@
 # URL:         https://github.com/junegunn/fzf
 # Author:      Junegunn Choi
 # License:     MIT
-# Last update: November 2, 2013
+# Last update: November 4, 2013
 #
 # Copyright (c) 2013 Junegunn Choi
 #
@@ -454,6 +454,8 @@ searcher = Thread.new {
           next if !new_search && !((vcursor-1)..(vcursor+1)).include?(idx)
 
           line, b, e = convert_item item
+          b ||= 0
+          e ||= 0
           row = cursor_y - idx - 2
           chosen = idx == vcursor