fix : Rapidly toggling element with out: transition causes incorrect node removal

[adiguba]

Fix #13681

On some rare case when a out transition is quickly canceled, the "dummy transition" onfinish can be executed after the cancel, and the node will be removed from the DOM.

It seems that setting onfinish back to noop fixes the problem.
However the bug is not systematic (the joys of race conditions), and I can't come up with a proper test for this.

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[trueadm]

We should have been doing this anyway, thank you.

[adiguba]

Sorry I forgot the changeset :/