Fix the crash caused by interface null value judgment error in golang.

[linrunqi08]

问题现象：
非容器场景，但是配置了容器的采集配置，golang模块会持续crash在docker client处

问题原因：
docker client为Interface类型，Go 语言规范规定：

• 接口变量仅当类型和值都为 nil 时才等于 nil
• 当接口持有具体类型的 nil 值时，接口本身不是 nil

修复方案：
initClient失败的时候，强制dc.client = nil，这样保证类型和值都为nil

[Copilot]

Pull Request Overview

This PR ensures the Docker client interface is fully reset on initialization errors to prevent stale non-nil interface values, and adds a test to verify error behavior across repeated initialization attempts.

• Explicitly set dc.client = nil when CreateDockerClient fails
• Added TestInitClientMutiTime to assert repeated initClient calls always error and leave client nil

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/helper/containercenter/container_center.go	Reset dc.client to nil on error in initClient
pkg/helper/containercenter/container_center_test.go	New TestInitClientMutiTime to validate repeated error behavior

Comments suppressed due to low confidence (2)

pkg/helper/containercenter/container_center_test.go:580

• [nitpick] Typo in test name: 'TestInitClientMutiTime' should be 'TestInitClientMultiTime' or 'TestInitClientMultipleTimes' for clarity and consistency.

func TestInitClientMutiTime(t *testing.T) {

pkg/helper/containercenter/container_center_test.go:581

• Missing coverage for the successful initialization path: consider adding a test that simulates a successful CreateDockerClient and verifies that initClient() sets client to a non-nil value and is idempotent on subsequent calls.

    containerCenterInstance = &ContainerCenter{}

[yyuuttaaoo]

这么看，通过依赖dc.client == nil来判断是否初始化本身可能就未必是Go语言推荐的做法，看起来是比较容易出错的