Procedure to bump an old Issue?

Hello,
I recently encountered an issue in CI's Query Builder, one that has been discovered by others before me, and already raised as a Pull Request (#4186).
However, I don't immediately see an Issue# for this, and it seems that their PR isn't consistent with the line numbering of CI 3.1.17.

I commented(#374227328) on the PR with my details & fix suggestion, but just want to check if this was the best place to leave this update, or if a fresh Issue would be best, or if I've just missed a link to the original one?
An additional complication is that the PR is from 2015 and seems to be tagged for CI 3.1, but clearly didn't make it in & get closed then. Yet also it appears tagged for 3.2 with the current minor code fix, rather than the one I explain would be better at handling all logical cases.

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It seems Narf has acknowledged your post on GitHub, so both places (Github and forums) would be inappropriate.

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