fixed compatibility with CocoonJS (launcher v1.4.7)

- CocoonJS does not support the `loadedmetadata` event, but only
`canplaythrough` and `ended`
- `node.readyState` is undefined when using CocoonJS
- `newNode.error` is undefined when using CocoonJS

(@see https://github.com/melonjs/melonJS/issues/470)