Added more checks (not really needed)

libs/lib/xaal/lib/aioengine.py

@@ -268,7 +268,7 @@ class AsyncEngine(core.EngineMixin):
         self.started_event.clear()
         # cancel all tasks
         for task in self.all_tasks():
-            if task != self._watchdog_task:
+            if task != self._watchdog_task and not task.cancelled():
                 task.cancel()
 
     def sigkill_handler(self, signal, frame):