Task to listen for canceled jobs is not properly stopped when job finishes about machine

[ddaspit]

This is most likely the cause of this issue: sillsdev/serval#84.

[johnml1135]

Really nice find. I added a "using" and also a check for the build state being "None". I believe that should be sufficient.

[ddaspit]

Yes, that would probably be sufficient, but the code should really be refactored further to ensure that the task is finished and everything has been properly disposed when the job completes. I will add a commit to the branch that adds the necessary changes.