title: get RadCartesianChart from grid(8x3) image issue when arrange
body: <p>im having a grid of 8x3 rows and col.below fetch me RadCartesianChart  and it generates a image in disk by the function "ExportCHARTtoBMP"</p>
  
  <pre><code>for (int row = 0; row &lt; (chartgridimage.RowDefinitions.Count())-1; row++)
      for (int column = 0; column &lt; chartgridimage.ColumnDefinitions.Count(); column++)
      {
          RadCartesianChart chart = chartgridimage.ChildrenOfType&lt;RadCartesianChart&gt;().FirstOrDefault(e =&gt; Grid.GetRow(e) == row &amp;&amp; Grid.GetColumn(e) == column);
          chart.Measure(new System.Windows.Size(470, 280));
          chart.Arrange(new Rect(0, 0, 470, 280));
          ExportCHARTtoBMP(chart,"chart"+row+""+column);
      }
  </code></pre>
  
  <p>export to bmp func:</p>
  
  <pre><code>private void ExportGRIDtoBMP(Grid gridinput, string filename)
  {
      gridinput.Measure(new System.Windows.Size(double.PositiveInfinity, double.PositiveInfinity));
      int grid1Width = (int)Math.Round(gridinput.ActualWidth);
      int grid1Height = (int)Math.Round(gridinput.ActualHeight);
      grid1Width = grid1Width == 0 ? 1 : grid1Width;
      grid1Height = grid1Height == 0 ? 1 : grid1Height;
  
      RenderTargetBitmap rtbmp = new RenderTargetBitmap(grid1Width, grid1Height, 96d, 96d, PixelFormats.Default);
      rtbmp.Render(gridinput);
      BmpBitmapEncoder encoder = new BmpBitmapEncoder();
      encoder.Frames.Add(BitmapFrame.Create(rtbmp));
      FileStream gridbmpfilestrm = File.Create(@"C:\Users\Admin\Desktop\" + filename + ".bmp");
      encoder.Save(gridbmpfilestrm);
      gridbmpfilestrm.Close();
      rtbmp.Clear();
  }
  </code></pre>
  
  <p>The issue is that when the image saved to disk, the line series is getting changed.</p>
  
  <p><img src="https://i.stack.imgur.com/pGezK.jpg" alt="Image"></p>