Fix possible ui 500 if workflow's job is nil (#31092)

Fix #31087

Author: lunny

options/locale/locale_en-US.ini

@@ -3638,6 +3638,7 @@ runs.pushed_by = pushed by
 runs.invalid_workflow_helper = Workflow config file is invalid. Please check your config file: %s
 runs.no_matching_online_runner_helper = No matching online runner with label: %s
 runs.no_job_without_needs = The workflow must contain at least one job without dependencies.
+runs.no_job = The workflow must contain at least one job
 runs.actor = Actor
 runs.status = Status
 runs.actors_no_select = All actors

routers/web/repo/actions/actions.go

@@ -107,7 +107,12 @@ func List(ctx *context.Context) {
 			// The workflow must contain at least one job without "needs". Otherwise, a deadlock will occur and no jobs will be able to run.
 			hasJobWithoutNeeds := false
 			// Check whether have matching runner and a job without "needs"
+			emptyJobsNumber := 0
 			for _, j := range wf.Jobs {
+				if j == nil {
+					emptyJobsNumber++
+					continue
+				}
 				if !hasJobWithoutNeeds && len(j.Needs()) == 0 {
 					hasJobWithoutNeeds = true
 				}
@@ -131,6 +136,9 @@ func List(ctx *context.Context) {
 			if !hasJobWithoutNeeds {
 				workflow.ErrMsg = ctx.Locale.TrString("actions.runs.no_job_without_needs")
 			}
+			if emptyJobsNumber == len(wf.Jobs) {
+				workflow.ErrMsg = ctx.Locale.TrString("actions.runs.no_job")
+			}
 			workflows = append(workflows, workflow)
 		}
 	}