Don't blow up if the tech is disposed before player.ready(). For #88.

The HLS tech waits until `ready` before setting the source to be sure that Flash has time to finish loading. If a user changed the src and triggered a tech unload before that time, the ready handler would be invoked, throw an exception, and leave the tech in a transitionary state. Instead, double check that the object element is still alive before setting the src in the `ready` handler.