fix: Avatar fallback bug

[afc163]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

close #25801

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Avatar not fallback correctly when src is invalid.
🇨🇳 Chinese	修复 Avatar src 图片地址失效时没有正确 fallback 的问题。

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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View rendered components/avatar/demo/fallback.md

[ant-design-bot]

[ant-design-bot]

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[codecov]

Codecov Report

Merging #25806 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #25806      +/-   ##
==========================================
- Coverage   99.51%   99.51%   -0.01%     
==========================================
  Files         369      369              
  Lines        7207     7201       -6     
  Branches     2018     1967      -51     
==========================================
- Hits         7172     7166       -6     
  Misses         35       35              

Impacted Files	Coverage Δ
components/avatar/index.tsx	100.00% <100.00%> (ø)

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