runner.pm: apply minor correctness fix

[vszakats]

"Lines 244-245 overwrite global variables $runnerr and $runnerw that
were already assigned in the child process (lines 205-206). In the
parent process context, these assignments appear incorrect and could
cause issues if runner_init is called multiple times. The parent
should only store references in the controller hashes."

It could never cause an actual issue, but clarifies the intent of the
code.

Spotted and fixed by GitHub Code Quality

Cherry-picked from #21646

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https://github.com/curl/curl/pull/21672/files?w=1

[Copilot]

Pull request overview

This PR prevents the parent/controller process from overwriting runner-side pipe globals when runners are initialized in multiprocess mode.

Changes:

• Limits $runnerr and $runnerw assignment to integrated single-process mode.
• Preserves per-runner controller pipe storage for both modes.

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[dfandrich]

"Lines 244-245 overwrite global variables $runnerr and $runnerw that were already assigned in the child process (lines 205-206). In the parent process context, these assignments appear incorrect

They seem to me to be unnecessary, but harmless.

and could cause issues if runner_init is called multiple times.

I don't see that as ever being an issue. This function isn't casually called to initialize an empty struct but rather to spawn a new worker, which has side effects that would be hard to ignore.

The parent should only store references in the controller hashes."

This patch may help clarify the intent of the code, since $runnerr and $runnerw in the parent are never accessed in $multiprocess mode. So I would be fine to apply it.

Spotted and fixed by GitHub Code Quality

Cherry-picked from #21646

https://github.com/curl/curl/pull/21672/files?w=1

[vszakats]

Thanks for reviewing, Dan. I've merged!