fix(select): invalidate when 'multiple`, `required` and model is `[]`

When `multiple` attribute is set on a `<select>` control and the model value is an empty array,
we should invalidate the control.  Previously, this directive was using incorrect logic for
determining if the model was empty.

Closes #5337
Merge branch 'master' of https://github.com/angular/angular.js
componentizd!