fix(pkg_auto): guard against IndexError on empty free_form_lines in get_batches()

[mohitjeswani01]

description

In pkg_auto/impl/sort_packages_list.py, the get_batches() method accessed
free_form_lines[-1] without checking if the list was non-empty first. When a
comment block contained package lines but no preceding free-form lines,
free_form_lines would be empty and the while condition would raise
IndexError: list index out of range.

Fix is a one-word guard added to the while condition:
while free_form_lines and not free_form_lines[-1]:

Fixes flatcar/Flatcar#2342.

How to use

Review the single-line change in pkg_auto/impl/sort_packages_list.py line 109.
No setup required — the fix is self-evident from the diff.

Testing done

Verified the fix by code reading. The guard free_form_lines and short-circuits
evaluation when the list is empty, preventing the IndexError.

python -m py_compile pkg_auto/impl/sort_packages_list.py

Output: Exit code 0 (no syntax errors)

• Changelog entries added in the respective changelog/ directory
• Inspected CI output for image differences

[Copilot]

Pull request overview

Guards Reader.get_batches() against an IndexError when free_form_lines is empty while trimming trailing blank lines from comment batches.

Changes:

• Add a short-circuit check to the while condition so free_form_lines[-1] is only evaluated when the list is non-empty.

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