Restore manual play call

Autoplay was causing some racy conditions when loaded with subtitle uri. Make it play after uri loaded signal, but still prevent going from stopped to play 2nd time.

src/player.js

@@ -584,6 +584,8 @@ class ClapperPlayer extends GstClapper.Clapper
     {
         debug(`URI loaded: ${uri}`);
         this.needsTocUpdate = true;
+
+        player.play();
     }
 
     _onPlayerWarning(player, error)