[filtede98]

Summary of Changes

This patch improves API stability and robustness across libyaml public interfaces by adding defensive NULL pointer checks:

• yaml_get_version: Allow callers to query only specific components (e.g., major, minor, or patch) by safely checking pointer arguments before writing.
• Parser and Emitter Lifecycle: Add NULL pointer validations in initialization, deletion, stream setup, and configuration functions (yaml_parser_initialize, yaml_parser_delete, yaml_parser_set_*, yaml_emitter_initialize, yaml_emitter_delete, yaml_emitter_set_*).
• Document and Event Management: Ensure functions handling event initialization/deletion and document creation/node addition safely guard against NULL parameters.
• Engine Entrypoints: Add defensive NULL guards to yaml_parser_parse, yaml_parser_scan, yaml_emitter_emit, yaml_emitter_open, yaml_emitter_close, yaml_emitter_dump, and yaml_parser_load.
• Tests: Extended tests/test-version.c with unit assertions validating NULL safety across the updated functions.

[filtede98]

Closing this PR as it hasn't received feedback and the NULL guards are defensive only. Thanks for maintaining the project!