Type: bug report

Describe what happened (or what feature you want)

We use sentinel in Spring Cloud Gateway, and found that when backend response incorrently,  SentinelReactorSubscriber will produce `IllegalReferenceCountException: refCnt: 0, decrement: 1`.

StackTrace

Operator called default onErrorDropped
reactor.core.Exceptions$BubblingException: io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
	at reactor.core.Exceptions.bubble(Exceptions.java:173)
	at reactor.core.publisher.Operators.onErrorDropped(Operators.java:635)
	at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.runFinally(FluxDoFinally.java:159)
	at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onComplete(FluxDoFinally.java:139)
	at com.alibaba.csp.sentinel.adapter.reactor.SentinelReactorSubscriber.hookOnComplete(SentinelReactorSubscriber.java:136)
	at com.alibaba.csp.sentinel.adapter.reactor.InheritableBaseSubscriber.onComplete(InheritableBaseSubscriber.java:191)
	at com.alibaba.csp.sentinel.adapter.reactor.SentinelReactorSubscriber.onComplete(SentinelReactorSubscriber.java:37)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:189)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onComplete(MonoFlatMap.java:260)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:252)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:207)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onComplete(MonoPeekTerminal.java:292)
	at org.springframework.http.server.reactive.ChannelSendOperator$WriteCompletionBarrier.onComplete(ChannelSendOperator.java:423)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:81)
	at reactor.core.publisher.FluxConcatArray$ConcatArraySubscriber.onComplete(FluxConcatArray.java:191)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:207)
	at reactor.netty.channel.MonoSendMany$SendManyInner.run(MonoSendMany.java:345)
	at reactor.netty.channel.MonoSendMany$SendManyInner.trySchedule(MonoSendMany.java:419)
	at reactor.netty.channel.MonoSendMany$SendManyInner.trySuccess(MonoSendMany.java:562)
	at reactor.netty.channel.MonoSendMany$SendManyInner.trySuccess(MonoSendMany.java:114)
	at io.netty.util.internal.PromiseNotificationUtil.trySuccess(PromiseNotificationUtil.java:48)
	at io.netty.channel.ChannelOutboundBuffer.safeSuccess(ChannelOutboundBuffer.java:717)
	at io.netty.channel.ChannelOutboundBuffer.remove(ChannelOutboundBuffer.java:272)
	at io.netty.channel.ChannelOutboundBuffer.removeBytes(ChannelOutboundBuffer.java:352)
	at io.netty.channel.epoll.AbstractEpollChannel.doWriteBytes(AbstractEpollChannel.java:364)
	at io.netty.channel.epoll.AbstractEpollStreamChannel.writeBytes(AbstractEpollStreamChannel.java:260)
	at io.netty.channel.epoll.AbstractEpollStreamChannel.doWriteSingle(AbstractEpollStreamChannel.java:471)
	at io.netty.channel.epoll.AbstractEpollStreamChannel.doWrite(AbstractEpollStreamChannel.java:429)
	at io.netty.channel.AbstractChannel$AbstractUnsafe.flush0(AbstractChannel.java:953)
	at io.netty.channel.epoll.AbstractEpollChannel$AbstractEpollUnsafe.flush0(AbstractEpollChannel.java:557)
	at io.netty.channel.AbstractChannel$AbstractUnsafe.flush(AbstractChannel.java:917)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.flush(DefaultChannelPipeline.java:1372)
	at io.netty.channel.AbstractChannelHandlerContext.invokeFlush0(AbstractChannelHandlerContext.java:750)
	at io.netty.channel.AbstractChannelHandlerContext.invokeFlush(AbstractChannelHandlerContext.java:742)
	at io.netty.channel.AbstractChannelHandlerContext.flush(AbstractChannelHandlerContext.java:728)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.flush(CombinedChannelDuplexHandler.java:531)
	at io.netty.channel.ChannelOutboundHandlerAdapter.flush(ChannelOutboundHandlerAdapter.java:125)
	at io.netty.channel.CombinedChannelDuplexHandler.flush(CombinedChannelDuplexHandler.java:356)
	at io.netty.channel.AbstractChannelHandlerContext.invokeFlush0(AbstractChannelHandlerContext.java:750)
	at io.netty.channel.AbstractChannelHandlerContext.invokeFlush(AbstractChannelHandlerContext.java:742)
	at io.netty.channel.AbstractChannelHandlerContext.flush(AbstractChannelHandlerContext.java:728)
	at reactor.netty.channel.MonoSendMany$SendManyInner$AsyncFlush.run(MonoSendMany.java:758)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
	at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:384)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)
Caused by: io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
	at io.netty.util.internal.ReferenceCountUpdater.toLiveRealRefCnt(ReferenceCountUpdater.java:74)
	at io.netty.util.internal.ReferenceCountUpdater.release(ReferenceCountUpdater.java:138)
	at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:100)
	at io.netty.buffer.AbstractPooledDerivedByteBuf.deallocate(AbstractPooledDerivedByteBuf.java:86)
	at io.netty.buffer.AbstractReferenceCountedByteBuf.handleRelease(AbstractReferenceCountedByteBuf.java:110)
	at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:100)
	at org.springframework.core.io.buffer.NettyDataBuffer.release(NettyDataBuffer.java:320)
	at org.springframework.cloud.gateway.filter.RemoveCachedBodyFilter.lambda$filter$0(RemoveCachedBodyFilter.java:43)
	at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.runFinally(FluxDoFinally.java:156)
	... 46 more

Describe what you expected to happen

Can sentinel handle this kind of exception, or should I handle it through Hooks.onErrorDropped by myself.

How to reproduce it (as minimally and precisely as possible)

1. backend service response incorrent.

Tell us your environment

spring-cloud-starter-gateway : 2.2.8.RELEASE
spring-cloud-alibaba-sentinel-gateway : 2.2.3.RELEASE
sentinel-reactor-adapter : 1.8.0