fix(module: textarea-item): fix textarea-item value protect

[nuonuoge]

PR Checklist

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• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd-mobile/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

[codecov]

Codecov Report

Merging #331 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #331      +/-   ##
==========================================
+ Coverage   89.58%   89.61%   +0.02%     
==========================================
  Files         229      229              
  Lines        6873     6882       +9     
  Branches      561      563       +2     
==========================================
+ Hits         6157     6167      +10     
+ Misses        552      550       -2     
- Partials      164      165       +1

Impacted Files	Coverage Δ
...omponents/textarea-item/textarea-item.component.ts	98.64% <100%> (ø)	⬆️
components/core/services/popup.service.ts	80.48% <0%> (-3.89%)	⬇️
components/picker/picker.component.ts	82.35% <0%> (+1.76%)	⬆️
components/picker/picker.service.ts	94.44% <0%> (+5.55%)	⬆️

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[nuonuoge]

@sWhite01111 https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/typeof
它返回的是字符串

[sWhite01111]

恩 我没有仔细看，前面加typeof是对的