fix(module:timeline): when the data clear, reset items

[to0simple]

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: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

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[to0simple]

#7030

[codecov]

Codecov Report

Merging #7109 (7001145) into master (d9982e9) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7109      +/-   ##
==========================================
- Coverage   89.63%   89.61%   -0.02%     
==========================================
  Files         488      488              
  Lines       15873    15875       +2     
  Branches     2584     2584              
==========================================
- Hits        14227    14226       -1     
- Misses       1014     1015       +1     
- Partials      632      634       +2     

Impacted Files	Coverage Δ
components/timeline/timeline.component.ts	98.14% <100.00%> (+0.07%)	⬆️
components/core/util/text-measure.ts	89.47% <0.00%> (-1.76%)	⬇️
components/time-picker/time-holder.ts	95.78% <0.00%> (-1.06%)	⬇️

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[wzhudev]

Hi. Thanks for this PR. Could you please add a test to ensure code coverage?

[to0simple]

Hi. Thanks for this PR. Could you please add a test to ensure code coverage?

I've added a test.

[wzhudev]

LGTM