fixed exception using defaults in constructors when creating lists

(issue #40)

Author: Ivan Lukic

TestStack.Dossier/Lists/ListBuilder.cs

@@ -20,10 +20,10 @@ public class ListBuilder<TObject, TBuilder>
 
         internal ListBuilder(int size)
         {
+            _list = new List<TBuilder>();
             BuilderProxy = (TBuilder) ListBuilderGenerator.Generator
                 .CreateClassProxy(typeof (TBuilder), new ProxyGenerationOptions(new EnsureAllMethodsVirtual()), new ListBuilderInterceptor<TObject, TBuilder>(this));
             BuilderProxy.ListBuilder = this;
-            _list = new List<TBuilder>();
             var fixture = new AnonymousValueFixture();
             for (var i = 0; i < size; i++)
                 _list.Add(new TBuilder {Any = fixture});