#dropdown{} option change

Hi,

  This is really minor change and considered not even doing a pull request for it.

  But if you use some restful forms/don't populate the value field of dropdown it can cause problems.

  This can be seen at the dropdown at http://nitrogenproject.com/demos/simplecontrols where the html renders everything as selected.

<select class="wfid_temp145757 dropdown"><option selected="">Dropdown</option><option selected="">Option 1</option><option selected="">Option 2</option><option selected="">Option 3</option></select>

  This is due the function selected_or_not/2 being passed Selected as [] instead of what it was trying to check i.e. undefined. And as you might not have filled in the value feild therefore it would be [] and match Selected.

  Hope this change request is not too minor, as I realise that it can be bypassed by using value and not only the text field of the #option{}.

Thanks Jesse.