Bar chart series selection is NULL for negative y axis value

What steps will reproduce the problem?
1.Draw chart with positive(100) & negative(-100) values for Y axis
2.Click on bar with positive value,we get series selection value.
3.But when we click on bar with negative value,We are getting NULL value for 
series selection.

What is the expected output? What do you see instead?
We should get series selection value of selected BAR.

Please provide a source code snippet that we can use to replicate the
issue.
SeriesSelection seriesSelection = graphView.getCurrentSeriesAndPoint();
        if (seriesSelection != null) {

            // Getting the y value after clicking BAR
        int amount = (int) seriesSelection.getValue();

        }

What version of the product binary library are you using?
achartengine 1.0.0

Please provide any additional information below.

Original issue reported on code.google.com by dattatra...@gmail.com on 3 Jul 2014 at 11:38

chenboling / achartengine

Bar chart series selection is NULL for negative y axis value #417