don't freak out if there's no config file present

Author: paulca

config/initializers/site_config.rb

@@ -1,5 +1,6 @@
 def site_config(key = nil)
-  config = HashWithIndifferentAccess.new(YAML.load(File.read("#{Rails.root}/config/site_config.yml")))
+  file = "#{Rails.root}/config/site_config.yml"
+  config = File.exists?(file) ? HashWithIndifferentAccess.new(YAML.load(File.read(file))) : {}
   return config[key] if key
   config
 end