fix issue with calling seek before onMetaData event in flash

I've been encountering an issue where the video is the incorrect size within the stage after switching resolutions when using the Flash tech.

![screenshot from 2014-07-09 16 28 53](https://cloud.githubusercontent.com/assets/225601/3534867/95056000-07f4-11e4-801c-837de6af59f7.png)

I tracked the problem down to NetStream.seek in ActionScript. If seek is called before the onMetaData event is fired, the onMetaData event will not be fired and the video will not be the correct size. Usually it's not a problem because the latency between the loadeddata event (which is fired first when the NetStream buffer is full) and the event in javascript is enough for the onMetaData event to fire. The problem can be worked around by listening to the loadedmetadata event instead when using flash.