fix #3975 (pie chart highlight disabled will lead to empty slice)

Source/Charts/Renderers/PieChartRenderer.swift

@@ -728,11 +728,6 @@ open class PieChartRenderer: DataRenderer
 
             guard let set = data.getDataSetByIndex(indices[i].dataSetIndex) as? IPieChartDataSet else { continue }
 
-            if !set.isHighlightEnabled
-            {
-                continue
-            }
-
             let entryCount = set.entryCount
             var visibleAngleCount = 0
             for j in 0 ..< entryCount
@@ -758,7 +753,7 @@ open class PieChartRenderer: DataRenderer
             let sliceAngle = drawAngles[index]
             var innerRadius = userInnerRadius
 
-            let shift = set.selectionShift
+            let shift = set.isHighlightEnabled ? set.selectionShift : 0.0
             let highlightedRadius = radius + shift
 
             let accountForSliceSpacing = sliceSpace > 0.0 && sliceAngle <= 180.0

Tests/Charts/PieChartTests.swift

@@ -70,4 +70,18 @@ class PieChartTests: FBSnapshotTestCase
         chart.drawCenterTextEnabled = false
         ChartsSnapshotVerifyView(chart, identifier: Snapshot.identifier(UIScreen.main.bounds.size), overallTolerance: Snapshot.tolerance)
     }
+
+    func testHighlightDisabled()
+    {
+        chart.data?.dataSets[0].highlightEnabled = false
+        chart.highlightValue(x: 1.0, dataSetIndex: 0, callDelegate: false)
+        ChartsSnapshotVerifyView(chart, identifier: Snapshot.identifier(UIScreen.main.bounds.size), overallTolerance: Snapshot.tolerance)
+    }
+
+    func testHighlightEnabled()
+    {
+        // by default, it's enabled
+        chart.highlightValue(x: 1.0, dataSetIndex: 0, callDelegate: false)
+        ChartsSnapshotVerifyView(chart, identifier: Snapshot.identifier(UIScreen.main.bounds.size), overallTolerance: Snapshot.tolerance)
+    }
 }