title: OpenCV color-value of a pixel by using mat.get() returns sometimes null
body: <p>I try to get the RGB Values of a pixel using mat.get(inx, int y) on Android and OpenCV 2.4.4.</p>
  
  <pre><code>Mat img = Utils.loadResource(getBaseContext(), R.drawable.ex3);
  double[] tmp = img.get(100, 100);
  if(printLog) Log.v(tag, "Color: "+ tmp[0] +","+ tmp[1] +","+ tmp[2] +"");
  </code></pre>
  
  <p>Normaly I got the tmp-Array returned. But at some pixels, i got returned "null". (That points are in range of the picture!)</p>
  
  <p>So why I get at some coordinates a array and on some others "null" and how to fix that?</p>