Fix crash when worker does not define #perform method

[kidlab]

Cloned from gohkhoonhiang#38

Problem

The /sidekiq_admin/adhoc-jobs/ endpoint will crash if one or more workers do not define #perform method. For example:

class DummyWorker
  include Sidekiq::Worker

  def perform(id)
  end
end

class DummyWorker2 < DummyWorker
end

Can verify in console by:

class_inspector = SidekiqAdhocJob::Utils::ClassInspector.new(DummyWorker2)
args = class_inspector.parameters(:perform)

NoMethodError: undefined method 'owner' for nil (NoMethodError)

        return method if method.owner == klass_name
                               ^^^^^^

We have to ugly workaround like this:

class DummyWorker2 < DummyWorker
  def perform(id)
    super(id)
  end
end