If no index passed to play API method - resume and return

Hi!

This pull request fixes the "TypeError: Cannot call method 'map' of undefined" error, which happens when you call flowplayer().play() API method (on any demo page). I've just added the return statement after player.resume() call.

How to reproduce this error:

Go to http://flowplayer.org/standalone/playlist/grid.html and open the console in dev tools.
Call flowplayer().play() and see the error:

![screen shot 2013-04-30 at 11 37 15 am](https://f.cloud.github.com/assets/576700/443312/b286c3b6-b17a-11e2-910c-87ea05974778.png)