[m-rev.] for review: Reset es_action field when idle ws engine receives a notification.

[Julien Fischer]

On Mon, 20 Apr 2020, Peter Wang wrote:

> In MR_do_idle_worksteal, reset the engine's es_action field to
> MR_ENGINE_ACTION_NONE before performing the notified action.
> This mirrors the behaviour in MR_do_sleep.
>
> Fixes the assertion failure in Mantis bug #461: when an engine is
> shut down, MR_verify_final_engine_sleep_sync checks that the engine's
> es_action field is MR_ENGINE_ACTION_NONE.
>
> runtime/mercury_context.c:
>    As above.
>
> NEWS:
>    Announce change.

That looks fine; presuambly this should be merged on to the release
branch as well?

Julien.