fix(module:auto-complete): reposition when open the first time

[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: #1840

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1863 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1863      +/-   ##
==========================================
+ Coverage   95.97%   95.98%   +<.01%     
==========================================
  Files         466      466              
  Lines       11217    11220       +3     
  Branches     1474     1475       +1     
==========================================
+ Hits        10766    10769       +3     
  Misses        131      131              
  Partials      320      320

Impacted Files	Coverage Δ
...auto-complete/nz-autocomplete-trigger.directive.ts	96.75% <100%> (+0.06%)	⬆️

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