fixed touch detection to select topmost spot. Spots are rendered in o…

…rder so the last spot in the list is on "top" for the viewer. If spots intersect, touch should return the upmost spot, which we accomplish by reversing the loop for touch selection.

lib/src/chart/scatter_chart/scatter_chart_painter.dart

@@ -364,7 +364,8 @@ class ScatterChartPainter extends AxisChartPainter<ScatterChartData> {
   ) {
     final data = holder.data;
 
-    for (var i = 0; i < data.scatterSpots.length; i++) {
+    for (var i = data.scatterSpots.length - 1; i >= 0; i--) {
+      // Reverse the loop to check the topmost spot first
       final spot = data.scatterSpots[i];
 
       final spotPixelX = getPixelX(spot.x, viewSize, holder);