ignore elements that are no longer in the document

[Rich-Harris]

closes #7876. This is an alternative to #7879 — the issue is that the click handler doesn't run until after Svelte has updated the DOM, meaning in some cases the element no longer exists in the DOM. In those cases it probably makes sense to bail altogether.

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[Rich-Harris]

We should probably merge #7828 first, since it touches a lot of this stuff

[dummdidumm]

style suggestion: do a if (..) return here instead, to safe some indentation (also I don't need to keep that if statement in my head as much)