[fix] [txn] Get previous position by managed ledger.

[thetumbled]

Motivation

Max read position is before the first ongoing txn's position. But the entry id of the first message may be 0, calculate the max read position by entry id - 1 is unsafe.

Modifications

Calculate the max read position by method managedLedger.getPreviousPosition.

Verifying this change

• [x] Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

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

If the box was checked, please highlight the changes

• [ ] 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

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

PR in forked repository: https://github.com/thetumbled/pulsar/pull/42