invoke error_handler on Committee::NotFound (#427)

My rationale is that an exception is raised if `raise` is true, but there is no opportunity to handle this error differently if otherwise.

lib/committee/middleware/request_validation.rb

@@ -20,6 +20,7 @@ def handle(request)
           raise if @raise
           return @error_class.new(400, :bad_request, $!.message, request).render unless @ignore_error
         rescue Committee::NotFound => e
+          handle_exception($!, request.env)
           raise if @raise
           return @error_class.new(404, :not_found, e.message, request).render unless @ignore_error
         rescue JSON::ParserError