Message chunking might not work in certain cases after PIP 132

[BewareMyPower]

Describe the bug
Sometimes a large message cannot be split into chunks and then failed to pass the isMessageSizeExceeded check. It's a bug introduced from PIP-132 (#14007).

To Reproduce

Add the following unit test to MessageChunkingTest:

    @Test
    public void testChunkSize() throws Exception {
        this.conf.setMaxMessageSize(100);

        final Producer<String> producer = pulsarClient.newProducer(Schema.STRING)
                .topic("my-property/my-ns/test")
                .enableChunking(true)
                .enableBatching(false)
                .create();
        producer.send(createMessagePayload(60));
    }

It will fail with

The producer test-0-0 of the topic persistent://my-property/my-ns/test sends a message with 102 bytes that exceeds 100 bytes

Expected behavior
It should not fail. Instead, this message should be split into two chunks and sent successfully.