fix lock scope to accept 0 params

refs CNVS-4706

Change-Id: I792e1bd911129bb3164b3972c8fafa25d85b3161
Reviewed-on: https://gerrit.instructure.com/18811
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Hetherington <clare@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

config/initializers/rails2.rb

@@ -114,6 +114,9 @@ ActiveRecord::Base.class_eval do
       with_exclusive_scope(:find => new_options) { all.map(&column) }
     end
   end
+
+  # support 0 arguments
+  named_scope :lock, lambda { |*lock| lock = [true] if lock.empty?; {:lock => lock.first} }
 end
 
 ActiveRecord::NamedScope::ClassMethods.module_eval do