Clean the pieces position when restarting the game

without that, the old pieces where still in game and this would break
the gameplay

app/src/main/java/school_project/Map.java

@@ -124,4 +124,13 @@ public class Map extends Shape{
             throw new RuntimeException(e);
         }
     }
+
+    /**
+     * set the position of each pieces in the map to null
+     */
+    public void resetPiecesPositions(){
+        for (Piece p : pieces) {
+            p.setPosition(null);
+        }
+    }
 }

app/src/main/java/school_project/Menu/ScreenLevelFinish.java

@@ -29,6 +29,7 @@ public class ScreenLevelFinish extends StackPane {
         ChooseLvl.setOnAction(event -> Controller.switchRoot(new MenuLevel(1)));
         retry.setOnAction(event -> {
             try {
+                lastlevel.resetPiecesPositions();
                 Controller.switchRoot(new GameUI(lastlevel));
             } catch (FileNotFoundException e) {
                 throw new RuntimeException(e);