[fix][client] Avoid NPE in Consumer.hasMessageAvailable() before calling receive() method

[oneby-wang]

Fixes: apache#25837

Motivation

Calling Consumer#hasMessageAvailable() before receiving any messages can hit a NullPointerException for a normal consumer because startMessageId may be null. In that state, hasMessageAvailable() should rely on the broker response and compare the mark-delete position instead of passing a null message id into hasMoreMessages.

Modifications

• Treat a null startMessageId as a subscription-position based consumer and fetch the latest message id response before deciding availability.
• Keep the inclusive seek behavior limited to consumers that actually start from MessageId.latest.
• Add coverage for hasMessageAvailable() before receive with default, earliest, and latest initial positions.

Verifying this change

This change added tests and can be verified as follows:

• ./gradlew :pulsar-client-original:compileJava
• ./gradlew :pulsar-broker:test --tests org.apache.pulsar.client.api.ConsumerCreationTest

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment