Fixed chunk_code_text's UnboundLocalError crash on empty code file

[jamesbraza]

If a code file is empty (e.g. a py.typed file), the Text-creation loop inside chunk_code_text will not be entered, so we hit an UnboundLocalError:

UnboundLocalError: cannot access local variable 'i' where it is not associated with a value

This PR:

• Fixes that crash, with test coverage
• Improves variable names and documents the purpose of conditional logic

[Copilot]

Pull Request Overview

This PR fixes an UnboundLocalError in chunk_code_text when processing empty files and improves the code’s variable naming.

• Fixes a bug where an empty file (e.g. py.typed) would trigger an UnboundLocalError.
• Enhances variable names and updates the logic in the chunking loop to improve clarity.
• Adds test coverage to verify the handling of empty file content.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/test_paperqa.py	Added a test case for a py.typed file to cover empty content scenarios.
paperqa/readers.py	Updated variable names in the chunking logic to prevent crashes and improve clarity.

Comments suppressed due to low confidence (2)

paperqa/readers.py:225

• [nitpick] Consider renaming 'last_line_i' to 'start_line_index' or a similarly clear name to better indicate its purpose in marking the start of a chunk.

line_i = last_line_i = 0

paperqa/readers.py:222

• [nitpick] Consider updating the function docstring to mention the use of the 'text_buffer' variable and the revised variable names for better clarity.

'''Parse a document into chunks, based on line numbers (for code).'''