[fix][misc] NPE during standalone shutdown

[nicoloboschi]

Motivation

java.lang.NullPointerException: Cannot invoke "org.apache.bookkeeper.common.component.LifecycleComponent.close()" because "bookie" is null
	at org.apache.pulsar.zookeeper.LocalBookkeeperEnsemble.stop(LocalBookkeeperEnsemble.java:501) ~[pulsar-broker-3.2.2.jar:3.2.2]
	at org.apache.pulsar.PulsarStandaloneStarter.lambda$new$0(PulsarStandaloneStarter.java:123) ~[pulsar-broker-3.2.2.jar:3.2.2]
	at java.lang.Thread.run(Thread.java:840) ~[?:?]

Modifications

• Fix NPE while closing pulsar standalone and bookies are not completed initialized yet

• doc-not-needed

[github-actions]

@nicoloboschi Please add the following content to your PR description and select a checkbox:

- [ ] `doc` <!-- Your PR contains doc changes -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->

[lhotari]

LGTM