[Backport release-0.3] Fix: fix panic when workflow is skipped

[FogDong]

Signed-off-by: FogDong dongtianxin.tx@alibaba-inc.com

Description of your changes

Fixes #

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Special notes for your reviewer

[codecov]

Codecov Report

Base: 24.53% // Head: 68.05% // Increases project coverage by +43.51% 🎉

Coverage data is based on head (66b9e5f) compared to base (bca032d).
Patch coverage: 33.33% of modified lines in pull request are covered.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-0.3     #124       +/-   ##
================================================
+ Coverage        24.53%   68.05%   +43.51%     
================================================
  Files               41       45        +4     
  Lines             3693     4019      +326     
================================================
+ Hits               906     2735     +1829     
+ Misses            2579      933     -1646     
- Partials           208      351      +143     

Flag	Coverage Δ
e2etests	24.53% <0.00%> (ø)
unit-test	65.58% <33.33%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/executor/workflow.go	81.26% <33.33%> (+51.01%)	⬆️
cmd/main.go	1.25% <0.00%> (ø)
pkg/utils/operation.go	72.72% <0.00%> (ø)
pkg/utils/test_utils.go	80.00% <0.00%> (ø)
pkg/utils/utils.go	80.32% <0.00%> (ø)
pkg/hooks/data_passing.go	54.54% <0.00%> (+9.09%)	⬆️
pkg/stdlib/packages.go	59.32% <0.00%> (+10.16%)	⬆️
pkg/generator/generator.go	68.54% <0.00%> (+10.48%)	⬆️
pkg/providers/providers.go	80.00% <0.00%> (+13.33%)	⬆️
pkg/tasks/template/load.go	75.67% <0.00%> (+16.21%)	⬆️
... and 27 more

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