title: draw a core-plot scatter-plot with a plot point gap
body: <p>Im relativly new to core plot and I stuck at some point. <br />
  I have a graph like this:<br/>
  <img src="https://i.stack.imgur.com/L7BSy.png" alt="enter image description here"></p>
  
  <p>and want to draw the graph with no gap, like the red dotted line shows!<br />
  How would you do that without drawing a plot symbol at this point?<br />
  It also should be possible to connect the to points if the value in Y is different!<br /><br />
  Has somebody dealed with that?<br />
  Thanks for any tip!</p>