Unset event handler when halting

[mjauvin]

This is supposed to run once, make it so in all cases.

[LukeTowers]

@mjauvin is this still needed? Can we have any unit tests added for this?

[mjauvin]

It's needed if we want a bindEventOnce() call that is also halting to be removed from the event listener array since the method returns before reaching the call that does this when $halting = false.

[mjauvin]

I'll see what I can do for a unit test.

[mjauvin]

@LukeTowers was able to add a unit test for this.

I tested commenting out the unset() statement and it does indeed fail the unit test.