block in replicator's _install_snapshot

[CkTD]

braft/src/braft/replicator.cpp

Lines 779 to 788 in e32b78a

	if (_options.snapshot_throttle && !_options.snapshot_throttle->
	add_one_more_task(true)) {
	return _block(butil::gettimeofday_us(), EBUSY);
	}
	// pre-set replicator state to INSTALLING_SNAPSHOT, so replicator could be
	// blocked if something is wrong, such as throttled for a period of time
	_st.st = INSTALLING_SNAPSHOT;

看注释，replicator 先把状态设置为 INSTALLING_SNAPSHOT，让后面的 throttle 等触发的 _block 可以正常执行。
但是实际 throttle 调用 _block 是在设置 INSTALLING_SNAPSHOT 前，这样会不会有问题？