Pulsar reader throws exception java.lang.IllegalStateException: recycled multiple times

[ErikJansenIRefact]

Describe the bug
A reader is created to read messages from a topic. The reader throws an exception when reader.readNext() is called.

To Reproduce

1. Messages are created with the attached CsvExample.java program (TPCH line item data is used as CSV file).
2. A reader is created and run with the attached ReaderExample.java program.
3. Most of the time the reader throws an exception, although sometimes it doesn't.
4. This is the output:

Num lines: 1000000
Message id: 71:99:-1:9999
Num lines: 2000000
Message id: 71:200:-1:9520
Exception in thread "main" java.lang.IllegalStateException: recycled multiple times
at org.apache.pulsar.shade.io.netty.util.Recycler$Stack.pop(Recycler.java:553)
at org.apache.pulsar.shade.io.netty.util.Recycler.get(Recycler.java:162)
at org.apache.pulsar.common.util.collections.BitSetRecyclable.create(BitSetRecyclable.java:1200)
at org.apache.pulsar.client.impl.PersistentAcknowledgmentsGroupingTracker.addBatchIndexAcknowledgment(PersistentAcknowledgmentsGroupingTracker.java:138)
at org.apache.pulsar.client.impl.ConsumerImpl.doAcknowledge(ConsumerImpl.java:551)
at org.apache.pulsar.client.impl.ConsumerBase.doAcknowledgeWithTxn(ConsumerBase.java:390)
at org.apache.pulsar.client.impl.ConsumerBase.acknowledgeCumulativeAsync(ConsumerBase.java:379)
at org.apache.pulsar.client.impl.ConsumerBase.acknowledgeCumulativeAsync(ConsumerBase.java:363)
at org.apache.pulsar.client.impl.ConsumerBase.acknowledgeCumulativeAsync(ConsumerBase.java:326)
at org.apache.pulsar.client.impl.ReaderImpl.readNext(ReaderImpl.java:119)
at ReaderExample.main(ReaderExample.java:19)

Expected behavior
The reader to read all messages instead of throwing an exception.
ReaderExample.java.zip
CsvExample.java.zip

Screenshots
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Desktop (please complete the following information):

• OS: iOS
• Pulsar: 2.6.0

Additional context
Add any other context about the problem here.

[sijie]

@codelipenghui can you take a look at this issue?