fix(module:tree, tree-select): fix the key validity check

[hsuanxyz]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #3163

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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[codecov]

Codecov Report

Merging #3247 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3247      +/-   ##
==========================================
+ Coverage   97.37%   97.39%   +0.01%     
==========================================
  Files         559      559              
  Lines       11627    11627              
  Branches      835      834       -1     
==========================================
+ Hits        11322    11324       +2     
  Misses        193      193              
+ Partials      112      110       -2

Impacted Files	Coverage Δ
components/tree/nz-tree-node.ts	93.38% <100%> (+1.47%)	⬆️
components/tree-select/nz-tree-select.component.ts	99.48% <100%> (ø)	⬆️
components/tree/nz-tree-base.service.ts	97.16% <100%> (-0.02%)	⬇️

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