Fix crash updating legislation process categories

We were expecting translation parameters in legislation processes
`update` action. However, those parameters aren't sent when we get to
that action through the "proposals" tab.

app/controllers/concerns/translatable.rb

@@ -8,6 +8,8 @@ module Translatable
   private
 
     def translation_params(resource_model)
+      return [] unless params[:enabled_translations]
+
       resource_model.translated_attribute_names.product(enabled_translations).map do |attr_name, loc|
         resource_model.localized_attr_name_for(attr_name, loc)
       end