[FLINK-40166][table] SQL query parsing fails if current catalog unreachable

[dalelane]

What is the purpose of the change

If the current catalog is unreachable, any SQL query fails to parse - even queries that make fully-qualified accesses to catalogs that are reachable.

This is because we make a call to databaseExists in the current catalog as part of parsing the statement.

Brief change log

This commit wraps the call to databaseExists in a try..catch so it doesn't block the remainder of the parsing.

Verifying this change

This change added tests and can be verified as follows:

• Added unit tests
• Manually verified using the attached recreate: flink-catalog-repro.zip

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes
  Generated-by: Claude Sonnet 5

[flinkbot]

CI report:

• d851f3d Azure: SUCCESS

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