fix: CobolResolve.java

* Clear references to child nodes after executing cancelCallStackList

Author: tsh-hashimoto

libcobj/app/src/main/java/jp/osscons/opensourcecobol/libcobj/call/CobolResolve.java

@@ -633,5 +633,6 @@ public static void cancelAll() throws CobolRuntimeException {
                     "Call to 'cancelAll' current stack is NULL");
         }
         cancelCallStackList(currentCallStackList.getChildren());
+        currentCallStackList.setChildren(null);
     }
 }