raft: remove IsEmptySnap check from raftLog.hasPendingSnapshot
raft: remove IsEmptySnap check from raftLog.hasPendingSnapshot

unstable.snapshot is never an empty snapshot. This check made it look
like it could be.

Signed-off-by: Nathan VanBenschoten <885ea01d97daf7784d4a0ae7f66c69a3686faeb6@gmail.com>

etcd-io/etcd,etcd-io/etcd,etcd-io/etcd