continuation pointer may be returned without being
written resulting in dispatching an invalid fiber pointer.
If a CQE is stolen but no fiber is blocked on the corresponding future
IoContext::getContinuationsFromCompletions will call
which will set the future's completion but will not return a continuation.
If no continuation is returned from
the continuation buffer is not advanced by
IoContext::reapSingleCompletion does not check if a continuation was
created and assumed that continuation contains a valid
a CQE was successfully stolen.
Initialize continuation with
nullptr, which is a valid