shard in ShardStateRecovering status never recover when restart

[hunjixin]

No description provided.

[hunjixin]

case OpShardRecover:
			if s.state != ShardStateErrored {
				err := fmt.Errorf("refused to recover shard in state other than errored; current state: %d", s.state)
				res := &ShardResult{Key: s.key, Error: err}
				d.dispatchResult(res, tsk.waiter)
				break
			}

OpShardRecover will check this problems

[hunjixin]

#120