don't use the result when hasn't set waker

leaf-server/src/main/java/org/dreeam/leaf/async/ai/Waker.java

@@ -11,6 +11,9 @@ public class Waker {
     public boolean state = true;
 
     public final @Nullable Object result() {
+        if (state) {
+            return null;
+        }
         Object result = this.result;
         this.result = null;
         return result;