修复 boneIdx 为 0 时的bug

[finscn]

用 boneIdx == null 代替 !boneIdx

Re: #

Changelog

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

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Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

Greptile Summary

This PR fixes a critical bug in the Spine skeleton socket binding logic where bone index 0 was incorrectly treated as missing due to JavaScript's falsy evaluation.

Key Changes

• Changed condition from !boneIdx to boneIdx == null in _updateSocketBindings() method
• Fixes bug where the first bone (index 0) would trigger an error and be skipped
• The _cachedSockets Map stores bone indices (numbers starting from 0), so !boneIdx would falsely evaluate to true when boneIdx is 0

Impact

This is a correct and important fix that ensures bones at index 0 can be properly used as socket attachment points in Spine animations.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The fix correctly addresses a classic JavaScript falsy value bug. The change from !boneIdx to boneIdx == null is the proper way to check for undefined/null values when 0 is a valid value. This is a single-line change with clear intent and no side effects.
• No files require special attention

Important Files Changed

Filename	Overview
cocos/spine/skeleton.ts	Fixed falsy check bug where boneIdx 0 was incorrectly treated as missing

Sequence Diagram

sequenceDiagram
    participant Client
    participant Skeleton
    participant _cachedSockets as _cachedSockets Map
    participant _socketNodes as _socketNodes Map

    Client->>Skeleton: _updateSocketBindings()
    Skeleton->>Skeleton: Check if _skeleton exists
    
    loop For each socket
        Skeleton->>Skeleton: Get socket.path and socket.target
        Skeleton->>_cachedSockets: get(socket.path)
        _cachedSockets-->>Skeleton: boneIdx (could be 0, undefined, or other number)
        
        alt boneIdx == null (NEW FIX)
            Skeleton->>Skeleton: error("path not found")
            Skeleton->>Skeleton: continue to next socket
        else boneIdx is valid (including 0)
            Skeleton->>_socketNodes: set(boneIdx, socket.target)
        end
    end
    
    Note over Skeleton,_socketNodes: Before fix: boneIdx=0 incorrectly triggered error<br/>After fix: boneIdx=0 properly sets socket binding

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Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1009738 bytes	1009738 bytes	✅ 0 bytes
2D All (legacy pipeline)	2675347 bytes	2675352 bytes	⚠️ +5 bytes
2D All (new pipeline)	2767083 bytes	2767088 bytes	⚠️ +5 bytes
(2D + 3D) All	10024081 bytes	10024086 bytes	⚠️ +5 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16843143 bytes	16843148 bytes	⚠️ +5 bytes

Interface Check Report

This pull request does not change any public interfaces !