Fix error in dialog_controller.js by checking for event before calling preventDefault

[jmarsh24]

There is a bug when rendering a dialog in the open state. The connect method tries to call preventDefault() on an event that doesn't exist which causes an error.

Steps to reproduce...

Render the following in a view template and you will get the following error
TypeError: Cannot read properties of undefined (reading 'preventDefault')

render RubyUI::Dialog.new(open: true) do
  render RubyUI::DialogContent.new do
    div do
      "hello"
    end
  end
end

This allows the event to be undefined and be able to open without issue.