fix: bugfix for predicate batch reader not check predicate nullptr

[lucasfang]

Purpose

Predicate nullptr is not checked. This may cause coredump when EnablePredicateFilter is on and no predicate is set.

Tests

PredicateBatchReaderTest, TestInvalidInput

API and Format

Documentation

[Copilot]

Pull request overview

This PR adds a null-check for PredicateBatchReader::Create() to prevent a crash when a null predicate is passed, and introduces a unit test covering that invalid input.

Changes:

• Add explicit nullptr validation for predicate in PredicateBatchReader::Create().
• Add a new unit test ensuring Create() fails with a clear error when predicate == nullptr.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/paimon/common/reader/predicate_batch_reader.cpp	Adds early validation to avoid null-dereference when creating a predicate batch reader.
src/paimon/common/reader/predicate_batch_reader_test.cpp	Adds a test case asserting Create() returns an error on null predicate.

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[lxy-9602]

+1