fix a bug: stopping a task might have caused an exception to appear in the browser console if the task was being re-enqueued.
fix a bug: stopping a task might have caused an exception to appear in the browser console if the task was being re-enqueued.

Weswit/utility-toolkit-javascript,Lightstreamer/utility-toolkit-javascript,Weswit/utility-toolkit-javascript,Lightstreamer/utility-toolkit-javascript