net: fix listening on FDs on Windows

Fix a bug introduced by 3da36fe of a missed early return of a handle
that needed to be passed to listen.

Fixes test-net-listen-fd0.js on Windows

lib/net.js

@@ -1060,8 +1060,7 @@ var createServerHandle = exports._createServerHandle =
     handle.open(fd);
     handle.readable = true;
     handle.writable = true;
-    return handle;
-
+    assert(!address && !port);
   } else if (port === -1 && addressType === -1) {
     handle = createPipe();
     if (process.platform === 'win32') {