fix panic when cpu or memory stress start time is nil

[xlgao-zju]

What problem does this PR solve?

What's changed and how it works?

Related changes

• Need to update chaos-mesh/website
• Need to update Dashboard UI
• Need to cheery-pick to release branches
  • release-2.1
  • release-2.0

Checklist

Tests

• Unit test
• E2E test
• No code
• Manual test (add steps below)
  create cpu or memory stress experiment, and then delete them. chaos controller will not panic

Side effects

• Breaking backward compatibility

Release note

Please add a release note.

You can safely ignore this section if you don't think this PR needs a release note.

DCO

If you find the DCO check fails, please run commands like below (Depends on the actual situations. For example, if the failed commit isn't the most recent) to fix it:

git commit --amend --signoff
git push --force

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• WangXiangUSTC
• iguoyr

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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[codecov]

Codecov Report

Merging #3104 (156f4c1) into master (079e42a) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3104      +/-   ##
==========================================
+ Coverage   38.02%   38.08%   +0.05%     
==========================================
  Files         106      106              
  Lines        9343     9343              
==========================================
+ Hits         3553     3558       +5     
+ Misses       5478     5472       -6     
- Partials      312      313       +1     

Impacted Files	Coverage Δ
pkg/workflow/controllers/chaos_node_reconciler.go	55.87% <0.00%> (-2.30%)	⬇️
.../workflow/controllers/workflow_entry_reconciler.go	55.02% <0.00%> (+6.87%)	⬆️

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[WangXiangUSTC]

LGTM

[iguoyr]

LGTM

[iguoyr]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 76e0f61

[ti-chi-bot]

@xlgao-zju: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[xlgao-zju]

/run-e2e-test

[xlgao-zju]

seems I can not re-trigger the test...

[iguoyr]

/run-e2e-tests