fix select options existence predicate
fix select options existence predicate

- `$el[0].options` would always evaluate to `true`
  even if the select object didn't have any option
  elements. So instead we're checking if the
  length is truthy.
- `selectedIndex` would evaluate to `true` because
  when there is no selected item `selectedIndex`
  equals `-1`

So in essence, stickit would try to get the
current selected option value even though there
were no options. This caused an issue on Internet
Explorer (tested in IE7 and IE8), where it would
fail when stickit tried to access the
`selectedIndex` of the select tag's options array.
Krasnyanskiy/backbone.stickit,adam-26/backbone.stickit,GerHobbelt/backbone.stickit,akre54/backbone.stickit,NYTimes/backbone.stickit,Krasnyanskiy/backbone.stickit,akre54/backbone.stickit,adam-26/backbone.stickit,NYTimes/backbone.stickit