Running mqtt benchmark triggers mqtt exception

[akrambek]

To Reproduce
Steps to reproduce the behavior:

1. Checkout https://github.com/aklivity/zilla-examples/tree/main/mqtt.kafka.broker and start the stack
2. Download the correct emqx-bench binary: https://github.com/emqx/emqtt-bench/releases
3. ./bin/emqtt_bench pub -c 100 -I 10 -t bench/%i -s 256 --shortids

org.agrona.concurrent.AgentTerminationException: java.lang.IndexOutOfBoundsException: index=0 length=24929 capacity=2
	at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.registry.DispatchAgent.doWork(DispatchAgent.java:707)
	at org.agrona.core/org.agrona.concurrent.AgentRunner.doDutyCycle(AgentRunner.java:291)
	at org.agrona.core/org.agrona.concurrent.AgentRunner.run(AgentRunner.java:164)
	at java.base/java.lang.Thread.run(Thread.java:1589)
Caused by: java.lang.IndexOutOfBoundsException: index=0 length=24929 capacity=2
	at org.agrona.core/org.agrona.concurrent.UnsafeBuffer.boundsCheck0(UnsafeBuffer.java:1692)
	at org.agrona.core/org.agrona.concurrent.UnsafeBuffer.boundsCheck(UnsafeBuffer.java:1698)
	at org.agrona.core/org.agrona.concurrent.UnsafeBuffer.putBytes(UnsafeBuffer.java:946)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.types.OctetsFW$Builder.set(OctetsFW.java:77)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.types.KafkaKeyFW$Builder.value(KafkaKeyFW.java:147)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.stream.MqttKafkaSessionFactory$KafkaSignalStream.lambda$onKafkaSessionExpirySignal$2(MqttKafkaSessionFactory.java:1067)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.types.stream.KafkaMergedDataExFW$Builder.key(KafkaMergedDataExFW.java:292)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.stream.MqttKafkaSessionFactory$KafkaSignalStream.lambda$onKafkaSessionExpirySignal$4(MqttKafkaSessionFactory.java:1066)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.types.stream.KafkaDataExFW$Builder.merged(KafkaDataExFW.java:384)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.stream.MqttKafkaSessionFactory$KafkaSignalStream.onKafkaSessionExpirySignal(MqttKafkaSessionFactory.java:1062)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.stream.MqttKafkaSessionFactory$KafkaSignalStream.onSignal(MqttKafkaSessionFactory.java:1047)
	at io.aklivity.zilla.runtime.binding.mqtt.kafka/io.aklivity.zilla.runtime.binding.mqtt.kafka.internal.stream.MqttKafkaSessionFactory$KafkaSignalStream.onSignalMessage(MqttKafkaSessionFactory.java:1035)
	at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.registry.DispatchAgent.handleReadInitial(DispatchAgent.java:1116)
	at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.registry.DispatchAgent.handleRead(DispatchAgent.java:1038)
	at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.concurent.ManyToOneRingBuffer.read(ManyToOneRingBuffer.java:181)
	at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.registry.DispatchAgent.doWork(DispatchAgent.java:701)
	... 3 more
	Suppressed: java.lang.Exception: [engine/data#0]	[0x0000000000000003] streams=[consumeAt=0x000c53f0 (0x00000000008c53f0), produceAt=0x000c54b0 (0x00000000008c54b0)]
		at io.aklivity.zilla.runtime.engine/io.aklivity.zilla.runtime.engine.internal.registry.DispatchAgent.doWork(DispatchAgent.java:705)
		... 3 more