fix: add missing target existence check to mind stone

src/main/java/uulm/teamname/marvelous/gamelibrary/gamelogic/GameLogic.java

@@ -139,6 +139,8 @@ public class GameLogic {
                             verifyCoordinates(state, data.targetField);
 
                             requireLineOfSight(state, data.originField, data.targetField);
+
+                            getAttackableWithoutID(state, data.targetField);
                         }
                         case RealityStone -> {
                             verifyCoordinates(state, data.targetField);