fix(select): ensure empty option is not lost in IE9

Fix a check inside render for select elements with ngOptions, which
compares the selected property of an element with it's desired state.
Ensure 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