fix(module:cascader): fix searching error when nzOptions is an empty …

[wzhudev]

…array

• update empty demos

close #2784

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
[x] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #2784

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[netlify]

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Built with commit 8cc14bc

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[codecov]

Codecov Report

Merging #2846 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2846      +/-   ##
==========================================
- Coverage    95.5%   95.49%   -0.01%     
==========================================
  Files         523      523              
  Lines       12236    12243       +7     
  Branches     1668     1669       +1     
==========================================
+ Hits        11686    11692       +6     
  Misses        197      197              
- Partials      353      354       +1

Impacted Files	Coverage Δ
components/cascader/nz-cascader.component.ts	95.74% <100%> (-0.16%)	⬇️

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[vthinkxie]

LGTM