[fix] prevent double decoding of params

[dmkret]

Closes #7515

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Latest commit: 53a01a8

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[dummdidumm]

Could you add a test that fails with the old way but succeeds with the fix?

[Rich-Harris]

thank you!

[benmccann]

Sorry I didn't get a chance to review this before it got merged, but it looks like this has a bug in it: #7554. Any chance you'd be able to take a look at it @dmkret ?

[dmkret]

@benmccann I'll take a look