Merge pull request #330 from StainlessStlRat/master

Prevent crash when updating datasets and calling animation functions

Author: hannesa2

MPChartLib/src/main/java/com/github/mikephil/charting/charts/Chart.java

@@ -761,8 +761,10 @@ protected void drawMarkers(Canvas canvas) {
 
 		for (Highlight highlight : mIndicesToHighlight) {
 
+			// When changing data sets and calling animation functions, sometimes an erroneous highlight is generated
+			// on the dataset that is removed. Null check to prevent crash
 			IDataSet set = mData.getDataSetByIndex(highlight.getDataSetIndex());
-			if (!set.isVisible()) {
+			if (set == null || !set.isVisible()) {
 				continue;
 			}