fix(module:cascader): fix not showing empty when there's no options

[wzhudev]

close #4562

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: #4562

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[codecov]

Codecov Report

Merging #4565 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4565      +/-   ##
==========================================
+ Coverage   93.17%   93.23%   +0.06%     
==========================================
  Files         521      519       -2     
  Lines       12844    12832      -12     
  Branches     2019     2016       -3     
==========================================
- Hits        11967    11964       -3     
+ Misses        461      452       -9     
  Partials      416      416

Impacted Files	Coverage Δ
components/cascader/nz-cascader.component.ts	95.41% <100%> (+0.12%)	⬆️
components/cascader/nz-cascader.service.ts	97.52% <100%> (ø)	⬆️
components/core/overlay/overlay-position.ts	92.3% <100%> (+0.64%)	⬆️
components/empty/nz-empty.service.ts	95.65% <0%> (-4.35%)	⬇️
...otification/nz-notification-container.component.ts	96.87% <0%> (-3.13%)	⬇️
...mponents/message/nz-message-container.component.ts	92.68% <0%> (-2.06%)	⬇️
components/typography/nz-typography.component.ts	98.23% <0%> (-0.89%)	⬇️
components/drawer/nz-drawer.component.ts	96.98% <0%> (-0.79%)	⬇️
components/time-picker/time-holder.ts	96.64% <0%> (-0.68%)	⬇️
components/tabs/nz-tabset.component.ts	93.1% <0%> (-0.32%)	⬇️
... and 20 more

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[hsuanxyz]

[cascader#搜索] demo 需要重新打开才会正确显示 empty

[wzhudev]

@hsuanxyz It should works now.