Fix applying lineCap value for line chart data sets (Fixes #3739)

DataSets for line chart have lineCap property which is supposed to be applied to the chart line. But it was applied only if dataSet is drawn in linear/stepped mode. This commit makes lineCap work for any existing mode.

Source/Charts/Renderers/LineChartRenderer.swift

@@ -73,6 +73,8 @@ open class LineChartRenderer: LineRadarRenderer
             context.setLineDash(phase: 0.0, lengths: [])
         }
 
+        context.setLineCap(dataSet.lineCapType)
+
         // if drawing cubic lines is enabled
         switch dataSet.mode
         {
@@ -313,8 +315,6 @@ open class LineChartRenderer: LineRadarRenderer
         }
 
         context.saveGState()
-
-        context.setLineCap(dataSet.lineCapType)
 
         // more than 1 color
         if dataSet.colors.count > 1