fix: 通过 API execute_job_plan 启动执行方案，如果传入的主机全局变量为空，Job 返回内部错误

[wangyu096]

Version / Branch / tag

3.7.x

出了什么问题？(What Happened?)

• 通过 API execute_job_plan 启动执行方案，如果传入的主机全局变量为空，Job 返回内部错误
• 传入参数

{"bk_scope_type":"biz","bk_scope_id":"1000","bk_biz_id":1000,"job_plan_id":2000,"global_var_list":[{"name":"target_hosts","server":{"ip_list":[]}}]}

• 异常信息

Caused by: feign.FeignException$BadRequest: [400] during [POST] to [http://job-manage/service/app/902/host/batchGet] [ServiceHostResourceClient#batchGetAppHosts(Long,ServiceBatchGetAppHostsReq)]: [{"success":false,"code":1241010,"errorType":2,"errorMsg":"请求参数[hosts]不合法，原因：hosts must not be empty","data":null,"requestId":"9490cfaded3eab716fe73efb06cf39cd","authResult":null,"errorDetail":null}]
	at feign.FeignException.clientErrorStatus(FeignException.java:213)
	at feign.FeignException.errorStatus(FeignException.java:194)
	at feign.FeignException.errorStatus(FeignException.java:185)
	at feign.codec.ErrorDecoder$Default.decode(ErrorDecoder.java:92)
	at com.tencent.bk.job.common.web.feign.FeignErrorDecoder.decode(FeignErrorDecoder.java:51)
	... 73 common frames omitted

[2023-07-03 15:01:12.683] ERROR [job-execute,377e6ae06f2a5c3de997f12117081b9e,da5de58c1cbc7c46] 30428 --- [http-nio-10502-exec-65] b.j.c.w.e.h.EsbExceptionControllerAdvice : Handle exception

java.lang.NullPointerException: null
	at com.tencent.bk.job.execute.service.impl.TaskExecuteServiceImpl.getServerValueFromVariable(TaskExecuteServiceImpl.java:1982)
	at com.tencent.bk.job.execute.service.impl.TaskExecuteServiceImpl.buildFinalTargetServers(TaskExecuteServiceImpl.java:1956)
	at com.tencent.bk.job.execute.service.impl.TaskExecuteServiceImpl.parseScriptStepInstanceFromPlanStep(TaskExecuteServiceImpl.java:1809)
	at com.tencent.bk.job.execute.service.impl.TaskExecuteServiceImpl.buildTaskInfoFromExecuteParam(TaskExecuteServiceImpl.java:1355)
	at com.tencent.bk.job.execute.service.impl.TaskExecuteServiceImpl.executeJobPlan(TaskExecuteServiceImpl.java:1202)
	at com.tencent.bk.job.execute.api.esb.v3.EsbExecuteJobPlanV3ResourceImpl.executeJobPlan(EsbExecuteJobPlanV3ResourceImpl.java:105)
	at com.tencent.bk.job.execute.api.esb.v3.EsbExecuteJobPlanV3ResourceImpl$$FastClassBySpringCGLIB$$4834dbc6.invoke(<generated>)

如何复现？(How to reproduce?)

1. 执行方案包含 1 个主机变量并且被引用
2. API 传入参数，主机变量为空（整个执行方案主机为空)

[wangyu096]

错误原因：执行方案的主机为空，去 job-manage 查询主机信息的时候，传入了空的主机列表，导致查询主机报错