[fix][broker] Fix NPE when ResourceGroupService execute scheduled task.

[Technoboy-]

Motivation

When the broker closes, the scheduled task in ResourceGroupService may still execute, and cause NPE:

Sep 17 12:09:50 168-15-22-49 pulsar[8900]: 2022-09-17T12:09:50,050+0800 [pulsar-2-4] ERROR org.apache.pulsar.common.util.Runnables - Unexpected throwable caught
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: java.lang.NullPointerException: null
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at org.apache.pulsar.broker.resourcegroup.ResourceGroupService.aggregateResourceGroupLocalUsages(ResourceGroupService.java:530) 
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at org.apache.pulsar.common.util.Runnables$CatchingAndLoggingRunnable.run(Runnables.java:54) 
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) ~[?:?]
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:305) ~[?:?]
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:305)
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[?:?]
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[?:?]
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) 
Sep 17 12:09:50 168-15-22-49 pulsar[8900]: at java.lang.Thread.run(Thread.java:829) ~[?:?]

Documentation

• doc-not-needed
  (Please explain why)

Matching PR in forked repository

PR in forked repository: (https://github.com/Technoboy-/pulsar/pull/6)