set isSnapped 4 spline

lib/process/primitives/area_abstract.dart

@@ -26,6 +26,7 @@ abstract class AreaItemAbstract extends MeasureItem<AreaItemFeatureAbstract> {
 }
 
 abstract class AreaItemFeatureAbstract extends MeasureItemFeature {
+  bool isSnapped = false;
   AreaItemFeatureAbstract(AreaItemAbstract refItem) : super(refItem);
 
   @override

lib/process/primitives/spline.dart

@@ -65,7 +65,7 @@ class Spline extends AreaItemAbstract with AutoSnapMixin {
       }
       doCalculate();
 
-      checkAutoSnap(args);
+      f.isSnapped = checkAutoSnap(args);
     }
     return true;
   }
@@ -99,7 +99,7 @@ class SplineFeature extends AreaItemFeatureAbstract {
   void paint(Canvas canvas, Size size) {
     if (innerPoints.isEmpty) return;
     final paintPoints = innerPoints;
-    if ((refItem as AutoSnapMixin).snapState) {
+    if (isSnapped) {
       paintPoints.removeLast();
     }
     drawId(canvas, size);