Unrendered sections does not throw when redefined and rendered in nested layout.

[ajaybhargavb]

Follow up #2226
For sections that are redefined but not rendered in the outer definition.

// NestedLayout
@{ Layout = "OuterLayout"; }
@section scripts {
   // stuff
}

// OuterLayout
@{ Layout = "BaseLayout"; }
@section scripts { 
  // Don't render inner scripts
}

// BaseLayout
@RenderSection("scripts");

In this scenario, the scripts section defined by NestedLayout is never rendered but the view would happily succeed.

cc' @pranavkm

[pranavkm]

I was already looking at a fix for this - should get a PR out for this in a bit.