Rethrow exceptions from RunAsync (#15034)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15034
Rethrow exception happened during RunAsync, ensure that pending tasks
are not executed after marked as finished
Reviewed By: andrewwdye
Differential Revision: D13409649
fbshipit-source-id: 3fd12b3dcf32af4752f8b6e55eb7a92812a5c057
