fix: handle missing original_path during placeholder resolution

[iamceeso]

Summary

Prevent AutoAPI from crashing when resolving placeholders with a missing or invalid original_path.

Currently _resolve_module_placeholders() assumes every placeholder contains a valid string original_path and unconditionally calls:

child["original_path"].rsplit(".", 1)

In some projects, malformed or unresolved placeholders may contain None, causing:

AttributeError: 'NoneType' object has no attribute 'rsplit'

This patch defensively validates original_path before use, logs a warning, removes the unresolved placeholder, and continues processing instead of aborting the build.

Result

• Prevents hard crashes during placeholder resolution
• Allows documentation generation to complete successfully
• Preserves existing behavior for valid placeholders

Validation

• Full tox suite passes
• Formatting, linting, typechecking, docs, and integration tests all pass