fix potential bug when setting filters via url param and not including fields

git-svn-id: https://dev.finn.de/svn/cockpit/branches/reporting_merge@1942 7926756e-e54e-46e6-9721-ed318f58905e

app/controllers/cost_reports_controller.rb

@@ -70,6 +70,7 @@ class CostReportsController < ApplicationController
   ##
   # Extract active filters from the http params
   def http_filter_parameters
+    params[:fields] ||= []
     (params[:fields].reject { |f| f.empty? } || []).inject({:operators => {}, :values => {}}) do |hash, field|
       hash[:operators][field.to_sym] = params[:operators][field]
       hash[:values][field.to_sym] = params[:values][field]