Fixes #6786 - Handle error when no taxonomy params get sent

Basically, no organization params are getting sent as the bug reporter is not
using json and not using wrapped params. You can also test this by doing:

curl -X POST http://localhost:3000/api/v2/organizations

This change prevents the following error from getting raised:

Processing by Api::V2::OrganizationsController#create as JSON
  Parameters: {"description"=>"biz", "name"=>"foo", "label"=>"bar", "apiv"=>"v2"}
Expire fragment views/tabs_and_title_records-1 (0.1ms)
Authorized user admin(Admin User)
undefined method `[]' for nil:NilClass (NoMethodError)
/usr/share/foreman/app/controllers/concerns/api/v2/taxonomies_controller.rb:75:in `params_match_database'
...