fix(pipeline): fix potiential panic

[d4x1]

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Summary

What does this PR do?
Fix a potiential panic.
When a blueprint is triggered, all pipelines behind it will be executed. If a pipeline is canceled manually. the running pipeline will still go on, and this will lead to a panic.

here are panic logs:

[GIN] 2023/11/19 - 22:18:08 | 201 |    10.36002ms |   {ip} | POST     "/blueprints"
time="2023-11-19 22:18:08" level=info msg="path /blueprints/3817/trigger will continue"
time="2023-11-19 22:18:08" level=info msg="try locking tables with timeout 2s"
[GIN] 2023/11/19 - 22:18:08 | 200 |   39.843051ms |   {ip} | POST     "/blueprints/3817/trigger"
time="2023-11-19 22:18:08" level=info msg="path /pipelines will continue"
[GIN] 2023/11/19 - 22:18:08 | 200 |   80.326947ms |   {ip} | GET      "/pipelines?blueprint_id=3817&page=1&pageSize=1&pending=1"
time="2023-11-19 22:18:08" level=info msg="path /pipelines/110925 will continue"
time="2023-11-19 22:18:08" level=info msg=" [pipeline service] get lock and wait next pipeline"
time="2023-11-19 22:18:08" level=info msg=" [pipeline service] run pipeline, 110925, now running runningParallelLabels are [parallel/jenkins_sync]"
[GIN] 2023/11/19 - 22:18:08 | 200 |   53.667161ms |   {ip} | DELETE   "/pipelines/110925"
time="2023-11-19 22:18:08" level=info msg=" [pipeline service] finish pipeline #110925, now runningParallelLabels is []"
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x170cb37]

goroutine 184483 [running]:
github.com/apache/incubator-devlake/core/runner.runPipelineTasks({0x20d86d0, 0xc002ab6750}, 0xc003ae8570?, {0xc005a57c18, 0x0, 0xadb90a?}, 0xc005a57dd8)
	/app/backend/core/runner/run_pipeline.go:93 +0x517
github.com/apache/incubator-devlake/core/runner.RunPipeline({0x20d86d0, 0xc002ab6750}, 0xc00283e450?, 0x1a86fa8?)
	/app/backend/core/runner/run_pipeline.go:53 +0x41b
github.com/apache/incubator-devlake/server/services.(*pipelineRunner).runPipelineStandalone(0xc005a57eb0)
	/app/backend/server/services/pipeline_runner.go:41 +0x65
github.com/apache/incubator-devlake/server/services.runPipeline(0xc002aa0f00?)
	/app/backend/server/services/pipeline_runner.go:113 +0x88
github.com/apache/incubator-devlake/server/services.RunPipelineInQueue.func1(0x1b14d, {0xc00310fa70?, 0xe42b26?, 0xc0046b1b00?})
	/app/backend/server/services/pipeline.go:264 +0x1c5
created by github.com/apache/incubator-devlake/server/services.RunPipelineInQueue
	/app/backend/server/services/pipeline.go:255 +0xa7
time="2023-11-19 22:18:11" level=info msg="plugin loaded sonarqube"
time="2023-11-19 22:18:11" level=info msg="plugin loaded sprint-performance-enricher"
time="2023-11-19 22:18:11" level=info msg="plugin loaded starrocks"
time="2023-11-19 22:18:11" level=info msg="plugin loaded tapd"
time="2023-11-19 22:18:12" level=info msg="plugin loaded teambition"
time="2023-11-19 22:18:12" level=info msg="plugin loaded trello"
time="2023-11-19 22:18:12" level=info msg="plugin loaded webhook"
time="2023-11-19 22:18:12" level=info msg="plugin loaded zentao"

Does this close any open issues?

Closes N/A

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Other Information

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