title: Highstock gapsize is causing line rendering issue
body: <p>I'm using Highstock (v4.2.3) to present data in a StockChart with a number of different Y axes, all plotted against time on the X axis. The data has gaps in it, and I'd like to depict those gaps, but when I turn on gapSize (with any value other than zero), there's a weird quirk that causes line rendering issues--when using the navigator to zoom in on certain date ranges (not all), in some cases (whose pattern I've yet to discern) the chart fails to fully render the line across the entire x axis.</p>
  
  <p>This <a href="http://www.screencast.com/t/sNYuPyCoZvb" rel="nofollow">annotated screenshot</a> depicts the issue.</p>
  
  <p>When I turn gapSize off (or explicitly set it to zero), this problem goes away. Note that the gaps themselves appear correctly on the chart (when navigating to a date range that doesn't present the line rendering issue). </p>
  
  <pre><code>plotOptions: {
      series: {gapSize:2}
  }
  </code></pre>
  
  <p>Any ideas?</p>