[C++] Avoid sending flow requests with zero permits

[BewareMyPower]

Motivation

When broker receives a FLOW request with zero permit, an IllegalArgumentException will be thrown in ServerCnx#handleFlow and then the connection will be closed so that the consumer will reconnect to the broker. If resumeMessageListener() was called for a zero queue consumer, the permits may be zero and trigger a reconnection. The frequent reconnections may cause messages repeated or out of order.

Modifications

• Validate the permits of a FLOW command before sending it.
• Add a test that a zero queue consumer resumes and pauses for each message periodically. Before this PR, there's a great chance that the received messages are repeated or out of order, even a ACK was sent.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests ZeroQueueSizeTest#testPauseResumeNoReconnection.

[BewareMyPower]

In addition to the PR description, when a zero queue consumer resumes, the broker's logs will be

22:12:52.953 [pulsar-io-52-21] WARN  org.apache.pulsar.broker.service.ServerCnx - [/127.0.0.1:58677] Got exception java.lang.IllegalArgumentException
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:128)
        at org.apache.pulsar.broker.service.Consumer.flowPermits(Consumer.java:524)
        at org.apache.pulsar.broker.service.ServerCnx.handleFlow(ServerCnx.java:1423)
        at org.apache.pulsar.common.protocol.PulsarDecoder.channelRead(PulsarDecoder.java:181)

[Anonymitaet]

@BewareMyPower Clear PR description! 👍