Fixed initial value not set from lambda expression when SelectList parameter is null.
- Fix https://aspnetwebstack.codeplex.com/workitem/853, DropDownListFor, value of lambda is not using in the initial display
- Finds the default value in a case where DropDownListFor() would not have selected any items i.e. when view data is used only for the SelectListItem enumeration
- Pull request from https://git01.codeplex.com/forks/shibayan/aspnetwebstack dropdownlist
- Three tiny deltas from original pull request: use existing ViewDataDictionary (one case) and use named parameters (two cases)

Original commit comment was:
Fixed: ListBoxFor and DropDownListFor don't selected value when SelectList parameter is null.
Had occurred in the following cases.

ViewBag.Foo = new SelectList(...);
@Html.DropDownListFor(model => model.Foo, null /* selectList is null */);

If you get a SelectList from the ViewData was to get the value from the ModelMetadata.