title: Detect JWPlayer is unable to play any given sources and show custom error message
body: <p>I'm using JWPlayer and passing a <code>.smil</code> source and a <code>.m3u8</code> source to the constructor:</p>
  
  <pre><code>var player = jwplayer("jwplayer-container");
  
  player.setup({
  
      ...
  
      sources: [
          {
              file: "some-rtmp-manifiest.smil"
          },
          {
              file: "some-hls-playlist.m3u8"
          }
      ],
  
      ...
  
  });
  </code></pre>
  
  <p>Unfortunately, if I view my player on a browser that doesn't support HLS or have Flash installed, I see an ugly and confusing error message in the player saying </p>
  
  <blockquote>
    <p>Error loading player: No playable sources found</p>
  </blockquote>
  
  <p>How can I detect this particular state in order to show my own error message (suggesting that the user installs Flash)?</p>