HRW: Bug where after an elif an else may be required

[zwoop]

This also fixes a small bug in run-plugin.

I think this may be a candidate for v10.1.x, but not 100% sure if all these things are in 10.1.x ?

[Issue discovered by Fina.]

[Copilot]

Pull Request Overview

Fix logic around incomplete rules in header_rewrite when encountering ELIF/ELSE blocks and correct a small argument handling bug in run-plugin initialization.

• Centralize rule-completion validation with a new helper to enforce constraints on ELIF/ELSE/OPER clauses without operators
• Adjust run-plugin argv population to iterate over token count rather than argc
• Minor parser/comment cleanups and a new ConditionGroup::has_conditions() helper

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
plugins/header_rewrite/parser.cc	Comment cleanup and small whitespace tweak; no functional change.
plugins/header_rewrite/operators.cc	Fix loop bound to use tokens.size() for argv population in run-plugin.
plugins/header_rewrite/header_rewrite.cc	Introduce validate_rule_completion and use it during parsing; adjust when rules are validated/transferred.
plugins/header_rewrite/conditions.h	Add has_conditions() to expose whether a group has any conditions.

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[cmcfarlen]

Put this back in the 10.1.x project. Great shame to the author for mixing unrelated bug fixes in one PR. :P