fix(select): placeholder (empty option) is lost in IE9

Fixes a check inside render for select elements with ngOptions, which compares the selected property of an element with it's desired state.
Ensured the placeholder, if available, is explicitly selected if the model value can not be found in the option list.
Without these fixes it's up to the browser implementation to decide which option to choose.
In most browsers, this has the effect of displaying the first item in the list. In IE9 however, this causes the select to display nothing.

Closes #2150, #1826