Querying improper season, episode selection should display error and random episode

[hawkins]

Should a season and episode combination not tie back to a real episode, a random episode should be selected and an error message should be shown on screen.

Something along the lines of...

if (season && episode) {
  this.state = {
    episode: getEpisodeDetails(season, episode)
  };
  if (this.state.episode === undefined) {
    // Display error
    // ...
    // Select random episode
    this.state.episode = getEpisodeDetails(season, episode);
  }
}

[hawkins]

Not sure how best to style this yet, so for now I've added a commit to make this issue at least load a random episode.