fix(module:rate): rate half value when allow half is false

[imaliouris]

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: #8535

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[zorro-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.58%. Comparing base (81ef077) to head (2b72f4e).
Report is 8 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8536   +/-   ##
=======================================
  Coverage   91.57%   91.58%           
=======================================
  Files         533      533           
  Lines       18336    18336           
  Branches     2801     2802    +1     
=======================================
+ Hits        16792    16793    +1     
  Misses       1226     1226           
+ Partials      318      317    -1     

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