Fix exists? to behave the same as find for numeric slugs

[sethbaugh]

If a record is created with a slug that is an integer (123, for example), Model.friendly.find("123") finds the correct record with slug of "123", but Model.friendly.exists?("123") returns false.

Referencing the comment here:

    # If the id is a numeric string like '123' it will first look for a friendly
    # id matching '123' and then fall back to looking for a record with the
    # numeric id '123'.

.find() is correctly finding the record by its slug "123". Code reference

    def find(*args)
      id = args.first
      return super if args.count != 1 || id.unfriendly_id?
      first_by_friendly_id(id).tap {|result| return result unless result.nil?}
      return super if potential_primary_key?(id)
      raise ActiveRecord::RecordNotFound, "can't find record with friendly id: #{id.inspect}"
    end

However, .exists? does not behave in the same way. It immediately passes to super looking for a record with an id of 123 based on .friendly_id?. Code reference

    def exists?(conditions = :none)
      return super unless conditions.friendly_id?
      exists_by_friendly_id?(conditions)
    end

I've updated .exists? to take a similar approach to find in looking for a record with the slug first and only passing it to super if none is found.

[parndt]

Thanks!