Make sure ViewerSelector.selectedKey always has a default value
Make sure ViewerSelector.selectedKey always has a default value

Before, `this.selectedKey` would be `undefined` if `localStorage.getItem()` threw an error (such as if the user has disabled localStorage, is in Private mode, etc.).

This commit assigns the `DEFAULT_VIEWER` value in the cases of `localStorage.getItem()` returning `undefined` AND throwing an Error.
immersive-web/webvr-polyfill,immersive-web/webvr-polyfill,marciot/webvr-polyfill,borismus/webvr-polyfill,borismus/webvr-polyfill,marciot/webvr-polyfill,jsantell/webvr-polyfill,jsantell/webvr-polyfill