prevent possible stack overflow due to recursive syntax support

namespace * Thrift.Test

struct Foo {
  1: Bar bar
}

struct Bar {
  1: Foo foo 
}

service ThriftTest
{
  i32 testRecursive(1: Foo foo);
}

var first = new Foo()
{
	Bar = new Bar()
	{
		Foo = new Foo()
		{
			Bar = new Bar()
			{
				Foo = null
			}
		}
	}
};

Console.Write("testRecursive(tree)");
Console.WriteLine(" = {0}", client.testRecursive(first));


Console.Write("testRecursive(ring)");
first.Bar.Foo.Bar.Foo = first;  // now let the innermost leaf backpoint to the root node
Console.WriteLine(" = {0}", client.testRecursive(first));

testRecursive(tree) = 4
testRecursive(ring)
Process is terminated due to StackOverflowException.