* DEV: Return 400 instead of 500 for invalid top period
This change will prevent a fatal 500 error when passing in an invalid
period param value to the `/top` route.
* Check if the method exists first
I couldn't get `ListController.respond_to?` to work, but was still able
to check if the method exists with
`ListController.action_methods.include?`. This way we can avoid relying
on the `NoMethodError` exception which may be raised during the course
of executing the method.
* Just check if the period param value is valid
* Use the new TopTopic.validate_period method
6ac3f1f7b5