Reset min/max when clearing ChartDataSet

ChartsOrg/Charts#3265

Author: danielgindi

MPChartLib/src/main/java/com/github/mikephil/charting/data/DataSet.java

@@ -61,27 +61,26 @@ public DataSet(List<T> values, String label) {
     @Override
     public void calcMinMax() {
 
-        if (mValues == null || mValues.isEmpty())
-            return;
-
         mYMax = -Float.MAX_VALUE;
         mYMin = Float.MAX_VALUE;
         mXMax = -Float.MAX_VALUE;
         mXMin = Float.MAX_VALUE;
 
+        if (mValues == null || mValues.isEmpty())
+            return;
+
         for (T e : mValues) {
             calcMinMax(e);
         }
     }
 
     @Override
     public void calcMinMaxY(float fromX, float toX) {
-
-        if (mValues == null || mValues.isEmpty())
-            return;
-
         mYMax = -Float.MAX_VALUE;
         mYMin = Float.MAX_VALUE;
+        
+        if (mValues == null || mValues.isEmpty())
+            return;
 
         int indexFrom = getEntryIndex(fromX, Float.NaN, Rounding.DOWN);
         int indexTo = getEntryIndex(toX, Float.NaN, Rounding.UP);