avoid the problem of cpu idling & fix wrong definition of error

[Mulavar]

What this PR does:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[LaurenceLiZhixin]

Good, this fixed the cpu idling if no node exist in zk problem.

[codecov-commenter]

Codecov Report

Merging #1629 (12cca45) into 3.0 (a8fba70) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

❗ Current head 12cca45 differs from pull request most recent head fe50cae. Consider uploading reports for the commit fe50cae to get more accurate results

@@            Coverage Diff             @@
##              3.0    #1629      +/-   ##
==========================================
- Coverage   41.08%   41.07%   -0.01%     
==========================================
  Files         253      253              
  Lines       14496    14493       -3     
==========================================
- Hits         5955     5953       -2     
+ Misses       7851     7850       -1     
  Partials      690      690              

Impacted Files	Coverage Δ
registry/zookeeper/listener.go	0.00% <0.00%> (ø)
remoting/zookeeper/client.go	0.00% <ø> (ø)
remoting/zookeeper/listener.go	0.00% <0.00%> (ø)
cluster/cluster/base/cluster_invoker.go	24.17% <0.00%> (-13.19%)	⬇️
metrics/prometheus/reporter.go	26.85% <0.00%> (-1.72%)	⬇️
metadata/report/delegate/delegate_report.go	35.09% <0.00%> (+8.60%)	⬆️

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[LaurenceLiZhixin]

这个会影响mesh router 的samples么？
2021-12-02T16:38:21.100Z ERROR v3router/uniform_rule.go:250 getRuleTargetInvokers from rule err = No invoker matches and no fallback destination to choose!
dubbo.apache.org/dubbo-go/v3/cluster/router/v3router.(*UniformRule).route
/home/runner/go/pkg/mod/github.com/!mulavar/dubbo-go/[email protected]/cluster/router/v3router/uniform_rule.go:250
dubbo.apache.org/dubbo-go/v3/cluster/router/v3router.(*UniformRouter).Route
/home/runner/go/pkg/mod/github.com/!mulavar/dubbo-go/[email protected]/cluster/router/v3router/uniform_route.go:52