Auto merge of #13600 - slester:13586, r=jdm

Invert conditional and return early for AddEventListener/RemoveEventL…

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Cleans up code as described in #13586 by returning early instead of nesting everything in an `if` statement.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13586

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- [x] These changes do not require tests because the change is a cleanup of code and the author of the issue stated that new tests were not required.

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…istener

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