Prevent double marks in IAB without unregistering the eventlistener

[Suven]

Hey,

thanks for your inspiring talk today at perfnow.nl! This recommendation came in really handy for me as I am using a SourcePoint but simply was missing out on this opportunity.

From my experience, publishers often already have code listening to that event because they need to process custom vendors, want to trigger reloads, or many other things. I imagine if someone stumbles upon your snippet and just adds the inner code to their existing callback, they might run into issues when unregistering the event handler. That's why I am suggesting this alternative.

On the other side, you could argue that this is the developers responsibility, or that they just could register two event listeners and thus, that this is a workaround for a problem that might not even exits in the first place.

In that case, I am not disappointed in you rejecting this PR. Take it as feedback/heads up in that case (:

[andydavies]

Thanks, I’ll take a look at this once I’ve caught up with a few other things I need to do