…4830)

Motivation:

We need to check if pendingUnencryptedWrites is null before accessing it
as the SslHandler might have been removed in the meantime.

```
io.netty.handler.codec.DecoderException: java.lang.NullPointerException: Cannot invoke "io.netty.handler.ssl.SslHandlerCoalescingBufferQueue.isEmpty()" because "this.pendingUnencryptedWrites" is null
	at io.netty.handler.ssl.SslHandler$SslTasksRunner.wrapIfNeeded(SslHandler.java:1798)
	at io.netty.handler.ssl.SslHandler$SslTasksRunner.safeExceptionCaught(SslHandler.java:1785)
	at io.netty.handler.ssl.SslHandler$SslTasksRunner.resumeOnEventExecutor(SslHandler.java:1896)
	at io.netty.handler.ssl.SslHandler$SslTasksRunner.access$2000(SslHandler.java:1751)
	at io.netty.handler.ssl.SslHandler$SslTasksRunner$2.run(SslHandler.java:1912)
	at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
	at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:405)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.NullPointerException: Cannot invoke "io.netty.handler.ssl.SslHandlerCoalescingBufferQueue.isEmpty()" because "this.pendingUnencryptedWrites" is null
	at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1503)
	at io.netty.handler.ssl.SslHandler.unwrapNonAppData(SslHandler.java:1469)
	at io.netty.handler.ssl.SslHandler.access$1800(SslHandler.java:170)
	at io.netty.handler.ssl.SslHandler$SslTasksRunner.resumeOnEventExecutor(SslHandler.java:1847)
	... 9 more
```

Modifications:

Add null check

Result:

Fix NPE